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Y12 APPLIED SCIENCE 1
Y12APPLIED SCIENCE
PLANT PROCESSES
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INDEX
4ASEXUAL REPRODUCTION IN FLOWERING PLANTS.......................................4
Types of Asexual Reproduction.................................................................................5SEXUAL REPRODUCTION IN FLOWERING PLANTS (Angiosperms).................9
POLLINATION.......................................................................................................14FERTILISATION........................................................................................................17
SEEDS......................................................................................................................22SEED STRUCTURE...........................................................................................22
SEED DISPERSAL.................................................................................................24PLANT STRUCTURE ................................................................................................27GERMINATION..........................................................................................................29
EXPERIMENT TO DETERMINE THE BEST CONDITIONS FOR GERMINATION..................................................................................................34
GROWTH....................................................................................................................35PRIMARY GROWTH.............................................................................................36SECONDARY GROWTH.......................................................................................38
FACTORS THAT AFFECT PLANT GROWTH................................................39TROPISMS..................................................................................................................41
THE IMPORTANCE OF NUTRIENTS..................................................................44PHOTOSYNTHESIS...................................................................................................49
PHOTOSYNTHESIS SUMMARY.........................................................................57STRUCTURE OF THE LEAF.....................................................................................58
STOMATA..........................................................................................................59CO2 ABSORPTION.............................................................................................61WATER AND SUGAR TRANSPORT...............................................................62
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Put them on your portable gadgets and “get one up” on those sat around you gossiping on the bus/train. You’ll know more and be able to remember more than them when it comes to exam time!!!
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Be able to list the asexual methods of reproduction which involve cuttings, tubers, rhizomes, runners and bulbsKnow the difference between seed dispersal and pollen dispersalBe able to give the typical structure of a wind or insect pollinated flower.Be able to say what the function of each part of a flower structure is.Know the steps involved from pollination to fertilisationBe able to describe the function of each of the structures in a dicotyledon seed.Be able to give examples of different methods of seed dispersalBe able to discuss the different germination stages.Know what environmental factors may affect germination and how germination is affected by them.Know how the meristematic tissue growsKnow how wind, temperature, moisture and oxygen affect the different plant processes.Be able to describe the difference between primary and secondary growth in roots and stems.Be able to discuss the importance of nutrients in growth and photosynthesis.Be able to draw and discuss the function of the parts of a dicotyledonous leaf.Know the photosynthesis equation Be able to list and discuss the factors that affect the rate of photosynthesis. Including light intensity, wavelength of light, temperature, amount of chlorophyll and carbon dioxide concentration.
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WHICH IS BEST; SEXUAL OR ASEXUAL REPRODUCTION?
ASEXUAL REPRODUCTION SEXUAL REPRODUCTION
Advantages Advantages
Disadvantages Disadvantages
ASEXUAL REPRODUCTION IN FLOWERING PLANTS
The flower contains the plants sex organs.
A flowering plant, by view of the fact that it has a flower, is capable of sexual reproduction. However, asexual reproduction in flowering plants is common. Why therefore would a plant capable of having sex want to produce clones by having sex with itself?
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There are lots of reasons why flowering plants may find this form of reproduction to their advantage.
If the environment has been stable for many generations, variability may not be as essential to the survival of the species. Asexual reproduction which is not as complex and requires far less energy, would be preferable.
When colonizing a new area, finding a mate for sexual reproduction may be difficult or impossible.
If the environment is particularly harsh, the more delicate or susceptible organs or stages of sexual reproduction may not be able to survive. Many plants which inhabit such areas as deserts or arctic tundra only reproduce asexually.
It is much, much quicker to reproduce asexually.
Types of Asexual Reproduction
1. Rhizomes
Plants such as grasses produce underground stems or rhizomes. As these stems grow through the soil, they randomly produce roots and a new shoot. If the rhizome dies, a new separate plant will have been formed
Rhizomes.
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2. Tubers
Tubers are actually modified rhizomes. They are formed in potatoes and kumara. They develop when specialized stem branches grow down into the ground and swell up with starch containing cells. Buds on the tubers will grow into new plants. Examine a potato tuber and note the buds which are commonly termed "eyes"
Potato Tubers.
3. Runners
These are horizontally growing stems that produce few, if any, leaves. At the spot where a leaf would normally develop a node, these plants will produce adventitious roots down into the soil, and new above ground shoots. Examine the strawberry plant or spider plant. Note the runner and the new shoots (Figure 8).
Runners/ Stolons.
4. Plantlets
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A few seed plants such as the duckweed and Kalanchoe sp. produce miniature plants on the edge of their leaves. These drop off and develop into mature plants. The duckweed, which is an aquatic plant, reproduces almost entirely by this method.
Plantlets.
5. Bulbs
Onions, chives and lilies over-winter in the form of a bulb. Each bulb has a very short stem which is surrounded by fleshy leaves. In the spring, the shoot apex begins to grow using the nutrients stored in the leaves.
Bulbs.
6. Corms
This structure is similar to bulbs except that there are no storage leaves. The nutrients are, instead, stored in the swollen stem. Gladiolus. and Crocus. produce corms
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Corms.
7. Cuttings
Many plants can reproduce asexually. That means that a new plant can start to grow when part of it is split off from the original 'parent' plant.
The new plant will be genetically identical to the parent plant.
This is what happens when a gardener takes a cutting to grow new plants.
Taking a plant cutting1) Take a disposable plastic cup and cut two small drainage holes in its base.
2) Three-quarters fill the cup with cutting compost.
3) Use a pot-plant such as a busy lizzie.
4) With a sharp knife, cut off one of the side branches. Cut the side branch just below the leaf closest to the main stem.This is the cutting.Take care with the knife.
5) Remove the bottom 2 or 3 leaves so that the cutting has a few leaves at the top. This helps stop the cutting losing too much water before the roots develop.
6) Gently push the cutting about 1–2cm into the compost.
7) Water the compost so it is moist but not soaking wet.
8) Place the cutting in a warm, well-lit positionsuch as a window.
9) The cutting should produce roots in 2–-3 weeks. Transfer it to a bigger pot and it will grow into a plant that is genetically identical to the one it was taken from.
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Cut just below where the leaf stem joins the side branch.
Push the cutting gently into the cutting compost.
Watching the roots developObserve the roots as they grow, place the cutting into a test tube. Add water so that the bottom 2cm of the shoot is in the water. You will be able to observe the roots developing over 2–3 weeks.
QUESTIONS
1. Did the cloned plant look identical to the parent plant? Why/why not?
SEXUAL REPRODUCTION IN FLOWERING PLANTS (Angiosperms)
The flower is the sexual organ of the plant. Most flowers are hermaphrodites. They have both male and female reproductive organs.
In 1759 Carl Linnaeus published a book on the sexual reproduction in plants. This caused an outcry and many clergymen wanted the book banned!!!
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Complete the table
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Structure Function
Petals
Anther
Filament
Stigma
Style
Ocary
Ovules
Sepal
Carpel
Stamen
Cut out the boxes below and arrange them under the correct headings on page 15
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This page left blank on purpose
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Assemble the flower here
NZQA QUESTION
a) Name ONE flowering plant that reproduces asexually, and describe its method of asexual reproduction.
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Method of asexual reproduction:
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b) Explain how asexual reproduction is different from sexual reproduction in flowering plants.
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c) Asexual reproduction in flowering plants has advantages and disadvantages. Discuss this statement with reference to reproduction and dispersal.
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NZQA QUESTION 6-05Many flowering plants can reproduce sexually and asexually (or vegetatively).a) Describe TWO ways a flowering plant can naturally reproduce asexually. (You may refer to named plants in your answer.)________________________________________________________________________
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b) Compare asexual and sexual reproduction in flowering plants and discuss how these two processes differ genetically.
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POLLINATION
WIND VERSUS INSECT
The structure of a flower will depend on whether it is pollinated by the wind or by insects.
Can you guess which is wind and insect from the pictures below?
What is the difference between the two flowers?_____________________________________________________________________
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Before fertilisation can occur, pollen must be transferred from one flower to another. This is pollination. The pollen grains must land on the stigma of another flower of the same type.
Below are some characteristics of insect and wind pollinated flowers. Next to each characteristic, explain why you think they have this characteristic.
INSECT POLLINATED FLOWERS
Flowers large and colourful or if the flowers are small, they grow in clusters.
Flowers produces scent
Flowers produce nectar.
Pollen grains are spiked or sticky.
WIND POLLINATED FLOWERS
Flowers are small and not often coloured.
Flowers produce no scent or nectar
Stamens and stigma hang out of the flower.
The stigma is feathery
Large amounts of light weight pollen is produced.
Although both male and female gametes are produced in the same flower, self-pollination does not normally occur. The flower will often produce the female and male gametes at different times.
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Insect Pollinated Wind Pollinated
Now have a look at this electron micrograph of a selection of different pollens
There are insect and wind borne pollen grains in this picture, can you pick out one of each?
NZQA QUESTION 4-05a) Give three characteristics of flowers that would attract insects for pollination.
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The photograph shows the male flowers of a deciduous tree. These are produced on the ends of the branches in early spring, before the new leaves appear
b) Explain how the position of the male flowers and the timing of flowering help pollination
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FERTILISATIONOnce a pollen grain has landed on the stigma a pollen tube grows out of the pollen grain and down the style to the ovule. The male nucleus then travels down this pollen tube, enters the ovule and fuses with the ovum. Fertilisation has occurred.
There are usually many ovules inside the ovary, so this means that many pollen must land on the stigma to fertilise each individual ovule.
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NZQA QUESTION 5 06The diagram below shows two types of flowers
Flower A Flower B
a) Name and describe the function of the flower parts labelled A to F in the diagram for Flower A.
NAME DESCRIPTIONA
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b) Explain why the stigmas in the two plants are different
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A
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c) Explain how the growth of a pollen tube leads to Fertilisation
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d) Discuss how the features of both flowers A and B allow pollination to occur (5 07)
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Draw what you see
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SEEDS
As soon as fertilisation has occurred some changes occur. The ovule grows and changes into the outside of the seed and a food source. The outside of the seed is called the testa - seed coat. Inside the seed a zygote starts dividing and developing into an embryo
The food source is important for the zygote, as it needs nourishment until it can make its own food. This isn’t until it has its own leaves.
Eventually the embryo develops three parts A radicle - young root A plumule – young shoot Cotyledons - seed leaves
In some plants the fruit wall (ovary wall) becomes soft and juicy, forming a fruit which is eaten by animals.
In dry fruits the ovary wall becomes tough and is not eaten. These seeds have to be dispersed by other means.
SEED STRUCTURE
Gently squeeze your bean seed to see if you can find where the water comes out. The little hole is called the micropyle. Note where the scar (hilum) is and look at the outer coating the testa.
Open the seed by slicing length wise and draw it.
A BEAN SEED
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Look for the baby plant and label the plumule and radicle. Then label the cotyledon and testa.
Put iodine on to the open seed. What do your results mean? How is this important?_____________________________________________________________________
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Slice a maize grain lengthways in half. Find the parts shown in the diagram below. Fill in the missing labels.
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Note the differences between this seed and the bean seed.
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Label each seed monocotyledon or dicotyledon.
SEED DISPERSALIt is preferable for seeds to be spread as far away (dispersed) from the parent plant as possible. This has two main advantages
The young plants do not have to compete with one another or with the parent for light, water and mineral salts.
The seeds may reach a better habitat than the parent.
There are four main methods of dispersal. By Wind seeds have wings, or hairs to catch the wind. E.g. dandelion By Animals seeds are carried inside edible fruits that are eaten by animals. Or
they are covered in hooks or barbs that attach to the animals fur or feathers. By Water this method is used by plants that grow near water such as coconuts
and mangroves. By Explosion in some plants the fruit splits open suddenly and violently,
flinging the seeds out as far as possible. E.g lupins, gorse.
Have a look at the pictures overleaf and determine how they are dispersed.
NZQA QUESTION
5-05The pea pod is the fruit of the pea plant. When mature the pod contains 8 – 10 seeds.
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(a) Name and describe how the parts of a pea flower develop into: (i) the pea pod.
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(ii) the pea seeds._____________________________________________________________________
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b)Explain how the production of fruit provides an advantage to the survival of flowering plants.
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7-06
During a class discussion the teacher said ‘pumpkins and lemons are both fruits’.
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Use the structure and development of fruit to explain why the pumpkin is biologically a fruit._____________________________________________________________________
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PLANT STRUCTURE – You do not need to know this section for your exam, but it will help you understand.
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GERMINATIONThe embryo inside the seed is in a state of dormancy. In this condition all metabolic processes have almost stopped. The embryo remains in this state until conditions are suitable for germination. Some seeds can remain dormant for many years, others only for a few days. Being able to survive for many years is obviously to the seeds advantage.
Gardeners sometimes have to artificially break the dormancy of seeds before they will grow. This many involve. Freezing, soaking, scraping or chipping.
To germinate seeds need Moisture Warmth Oxygen
The seed absorbs water and swells up. This causes the testa to split enabling the radicle and plumule to grow out of the seed. The water also activates enzymes in the seed that will convert stored starch into soluble molecules that can be transported to the growing tips of the radicle and plumule. The food that is supplied to the dividing cells is broken down by the process of respiration to release the energy that is needed for growth. This is why germinating seeds need oxygen.
The radicle grows first and after a day or two the plumule grows out from between the cotyledons. Until it reaches the surface it is pale yellow with very small leaves. It is also a hook shape which protects the delicate leaves as it grows through the soil. No matter which way the seed falls the radicle will always grow downwards and the plumule will always grow upwards. This is called geotropism.
Once the plumule reaches the surface it straightens out, the leaves expand and it becomes green as the chlorophyll develops. Until the plumule reaches the surface the seedling is dependent on food that it obtained from its parent. Once photosynthesis begins the plant is independent.
The temperature needed for germination varies. Seeds that germinate in the tropics require much warmer conditions than those from cooler regions.
Most seeds will grow just as well in the dark as in the light, but some seeds will only germinate in the dark, while others need light. Plant hormones play a vital role in germination and also in breaking seed dormancy.
QUESTIONS1. Why is it important for plants to spread their seeds?
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2. What special adaptations must seeds that are transported inside animals have?
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3. Mangrove seeds start to develop a root before they fall from the tree, why is this necessary?
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4. Describe the differences that are seen between the pollen of a wind-pollinated flower and that of an insect-pollinated flower. (Two differences required.
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5. Explain why the differences are required for successful pollination in each type of plant.
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6. Describe the difference between self-pollination and cross-pollination._____________________________________________________________________
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7. Explain the advantage that plants produced by cross-pollination have over plants produced by self-pollination. (Two ideas needed)
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8.
8-06
The diagram below compares a typical monocotyledon and dicotyledon seed.
a) Describe the function of the endosperm of a monocotyledon seed._____________________________________________________________________
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A seed only germinates in suitable environmental conditions.
b)Describe the TWO main environmental conditions necessary before a seed can germinate._____________________________________________________________________
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c) Explain how ONE structure of a seed enables it to survive for long periods of time, before it finally germinates.
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Plant a bean seed and watch it grow over a period of three weeks. Draw the stages of its development below.
What does this graph tell you? (Live mass is the mass of the living tissue plus the water that it has absorbed. Dry mass is the mass of the living tissue without the water)
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EXPERIMENT TO DETERMINE THE BEST CONDITIONS FOR GERMINATION
METHOD1. Place 6 seeds on the bottom of 4 labelled Petri dishes.2. Cover with a layer of cotton wool3. Apply 10mL of water to all but one dish. 4. Take the dish with no water and write your initials on the lid. Place in a warm
corner.5. To one of the other plates add oil over each seed to exclude oxygen.6. Initial this dish and place in a warm corner.7. To one of the other dishes write your initials and the word COLD on it. Place
on the front desk to put in the fridge8. To the remaining dish put your initials and the word DARK on it. Place on
the front desk to be put in a dark cupboard.9. Measure the average length of the stem after 1 week.
RESULTSConditions GrowthNo water
No warmthIn a fridge
No OxygenCovered in oil after water applied
No LightPut in a dark cupboard
CONCLUSION
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GROWTH
A typical plant consists of two parts, a root system that absorbs water and minerals and a shoot system that uses light energy to convert carbon dioxide and water into carbohydrates by phtosynthesis.
A fully developed shoot system consists of a stem bearing leaves. The leaves are formed at points called nodes. The area in between the nodes is called an internode.
At the tip of the shoot the young leaves are very small and clustered together to form a terminal bud. The stalk of a leaf is called the petiole and the angle between a petiole and the stem is called the leaf axil. In each axil there is an axillary bud which may grow out into a side shoot.
Flowering plants can be divided into two large groups.Monocotyledons like grasses, palms and lilies usually have parallel veins in the leaves.Dicotyledons include clover, buttercups, daisies and most flowering trees and have leaves whose leaf veins form a network.
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PRIMARY GROWTH
Growth in a length of stem or root is called primary growth. Growth by increasing the number of cells only occurs in the meristems tissue. i.e mitosis only occurs in the meristems.
Plants grow at the tips of their shoots and roots, so these areas are always the youngest parts. Both roots and shoots increase in length by cell division, and then cell enlargement. These processes take place in different regions.
Cell division takes place in the apical meristems at the tips of the shoot and root. Cells increase in numbers by mitosis.
Behind the tip the cells begin to enlarge. Further back still, the cells begin to differentiate. (specialise for particular
functions) For example in the root the outermost layer of cells develops long outgrowths called root hairs. These are specialised for absorbing water. In the shoot the cells on the surface specialise for water conservation by developing a waxy cuticle.
So there are three cell processes involved in growth……..division (mitosis), enlargement and specialisation.
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The apical meristem of the root is protected by a root cap. This is a mass of loose cells that are continually sloughed off and replaced by new cells as the young root pushes down into the soil.
Growth through the meristematic tissue causes elongation of stems and roots.
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SECONDARY GROWTH
Growth to increase stem and root girth is called secondary growth. This kind of growth takes lace in woody trees and shrubs but does not take place in herbaceous annuals and biennials which only live for one or two years.
Secondary growth takes place in both the stem and the root by division of meristematic cells located between the xylem and the phloem in the vascular part of the plant.
These meristematic cells are made up of the cambium, and are able to still undergo rapid mitosis.
The cambium is found in a series of small groups of cells wedged between the xylem and phloem. The first step in growth is the linking of these groups to form a ring of cambium tissue. This tissue separates the xylem and the phloem.
The cells now multiply. The cells on the inside of the cambium ring produce secondary xylem cells and the cells on the outside become secondary phloem cells.
Each year the cambium produces more secondary xylem and phloem. This causes growth rings. Growth rings are formed by the xylem and not the phloem. The Phloem is soft tissue and eventually is crushed.
Of course all this growth to make the stem thicker will split the outside protective covering. However, just beneath the epidermis a layer of cells called the cork cambium divides to form new surface tissues.
Plant hormones called auxins are responsible for controlling growth.
List the differences between primary and secondary growth.
Primary secondary
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FACTORS THAT AFFECT PLANT GROWTH
TEMPERATURETemperature will directly affect photosynthesis, respiration and transpiration (water loss). The warmer it is the faster these processes will occur.
MOISTURE Plant growth can be restricted by both low and high levels of moisture in the soil. Good moisture means that the plants can get their nutrients much easier. Too little moisture and the nutrients can not be dissolved, too much and the nutrients are washed away. In this case fertilisers will make no difference.
SUNLIGHTThe quality, intensity and duration of light are important in the way that they affect photosynthesis. Certain plants will behave in certain ways depending on the length of the day. This is called photoperiodism.
CARBON DIOXIDE LEVELSIncreasing the CO2 levels can increase the photosynthesis rate and hence improve crop yields.
Plants will grow quicker in warmer temperatures; however, high temperatures can cause growth to slow due to the effects of higher water loss.
The higher amount of water available in the spring and good temperature conditions results in larger xylem vessels being produced at that time of year and a more rapid growth spurt.
In the spring and summer, there is more sunlight, this means that there is more photosynthesis able to happen and so more glucose is produced. A lot of this glucose will be converted to starch and stored for later use.
NZQA QUESTION 4-07Different plant structures are built from specialised groups of plant cells called tissues. Each plant structure is made up of tissues designed to carry out specialised functions or processes.
The diagram shows the arrangement of plant tissues in a dicotyledon stem.
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Each year the stem will grow thicker by secondary thickening.a) Explain how the stem grows thicker._____________________________________________________________________
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Plant growth at the shoot tips and the root tips shows some similarities and some differences.b) Discuss reasons for the similarities and the differences in the way plants grow at the shoot tips compared with the root tips._____________________________________________________________________
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c) 9-06 Describe the function of cambium cells in a young green stem._____________________________________________________________________
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TROPISMSPlants respond to stimuli (changes in their surroundings) just like all living things.
A tropism is the growth of a plant part in a direction that depends on the direction of the stimulus.
A positive tropism is where the growth is towards the stimulus and a negative tropism is where the growth is away from the stimulus.
Most stems show positive phototropism, as they grow towards light. Plumules of seedlings show negative geotropism (Sometimes called
gravitropism) as they grow away from the direction of gravity. Radicles show positive geotropism as they grow in the direction of gravity. Climbing plants show thigmotropism, they bend towards anything they touch
and coil around it. Pollen tubes show positive chemotropism as they grown towards the
chemicals formed by the female gamete. Roots show positive hydrotropism as they grow towards water.
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Charles Darwin did some simple experiments to demonstrate phototropism in oat seedlings.
As in all grasses the first leaves are protected as they grow up through the soil by a spear like sheath called a coleoptile. When the coleoptiles were covered up, the grasses did not bend towards the light. When he covered the entire coleoptile, except the very tip the grasses still bent towards the light.
THEN
The part of the shoot that detected the light, appeared to be quite a way from the part of the shoot that did the bending. There must be some kind of communication system in the plant to allow this to happen.
Later on in that century scientists conducted more experiments
After cutting the tip off and replacing it, a coleoptile could still respond to light. Showing that the message could not be sent by nerves as they nerves would have been cut.
When the tip was separated from the base by a water-based jelly, the coleoptile curved normally. Showing that the message was being sent by chemicals.
When an impermeable membrane was inserted into the shaded side there was no response. When an impermeable membrane was inserted into the sunny side then the coleoptile bent. This showed that the messenger chemical travelled down the shaded side of the coleoptile.
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Light
THEN
The messenger chemical is called auxin.
Cause of PhototropismWhen a shoot is illuminated from one side, the auxin is transported down the shaded side, causing this side to elongate faster than the sunny side. This makes the shoot bend towards the light.
Cause of GeotropismIf a stem begins to grow along the horizontal, then the effect of gravity will cause the auxin to gather on the lower side. This in turn makes that side grow faster in a stem and the stem begins to grow upwards. In a root the auxin slows the growth so the lower side grows more slowly and the root grows downwards.
HOW TROPISMS HAPPENPlant growth is controlled by HORMONES. The growth hormone controlling tropisms is called ____________________________. and are only needed in very small amounts
ROOTS are much more sensitive to this hormone than SHOOTS.
The effect of auxin in a shoot showing PHOTOTROPISM
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Light
Explain how auxin causes the shoot tip to bend towards the light:
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THE IMPORTANCE OF NUTRIENTS
Plants need more than just water and carbon dioxide to grow. A number of essential minerals (elements) are needed.
Nitrogen – Important part of proteins, enzymes and chlorophyll. Without adequate supply the plant ceases to photosynthesise and dies.
Phosphorus – Helps with the transfer of solar energy into chemical energy. An important part of chlorophyll. Promotes good root growth. Also a part of proteins
Potassium - is absorbed by plants in larger amounts than any other mineral element except nitrogen and, in some cases, calcium. Helps in the building of protein, photosynthesis, fruit quality and reduction of diseases.
Calcium - Calcium, an essential part of plant cell wall structure, provides for normal transport and retention of other elements as well as strength in the plant. It is also thought to counteract the effect of alkali salts and organic acids within a plant.
Magnesium - Magnesium is part of the chlorophyll in all green plants and essential for photosynthesis. It also helps activate many plant enzymes needed for growth.
Sulfur - Essential plant food for production of protein. Promotes activity and development of enzymes and vitamins. Helps in chlorophyll formation. Improves root growth and seed production. Helps with vigorous plant growth and resistance to cold.
Summarise the above by writing the symbols for the elements under the titles below
Essential part of chlorophyll
Essential part of Proteins Essential part of crucial Enzymes
Improves growth Essential for photosynthesis
Essential part of cell wall
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NZQA QUESTION 7-05A child carved their initials deeply into the trunk of a tree, 1 metre above the ground, in 2005. Describe the probable position and appearance of the carved initials in 10 years time. _____________________________________________________________________
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8 05Describe how early seedling growth is affected by: (i) gravity
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3 07Plants need enough nitrogen for healthy growth. The diagram shows a plant that has grown in soil that did not have enough nitrogen in it.
Old leaves yellow, whole plant pale green
a) Explain how plants use nitrogen for healthy growth.
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PHOTOSYNTHESIS
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PHOTOSYNTHESIS
Photosynthesis is a process where plants take energy, carbon dioxide and water to make sugars. It is the opposite process to respiration.
The sugars are often stored as starch and are a plants energy reserves. These may be used for growth, reproduction and repair.
For photosynthesis to take place, a plant requires Water Light Carbon dioxide Suitable temperature Chlorophyll
We can test whether a plant has undergone photosynthesis by testing its leaves for starch.
TESTING A LEAF FOR STARCH
1. Place your plant in darkness for at least 24h to ensure that the plant has used up all the starch that it has stored in its leaves.
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2. Cover part of a leaf with some paper. Get creative; try fancy patterns or your initials.
3. Put the plant back into sunlight for at least 24h.
4. Cut off the leaf for testing.
5. Boil the leaf for one minute. This breaks down the cells and allows us access to the contents of the cells.
6. Then heat the leaf in alcohol until it is no longer green. This removes the chlorophyll.
7. Then drop iodine onto the leaf. Where starch is present the leaf will turn black.
QUESTIONS
1. Draw the paper shape that you put on your leaf here.
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2. Why did you boil the leaf in water, followed by heating it in alcohol?
3. What did the iodine test for?
4. Photosynthesis requires water, carbon dioxide and light. Which of these three things does this experiment prove is needed? How does it prove this?
EXPERIMENT TO SHOW THAT INTENSITY OF LIGHT AFFECTS THE RATE OF PHOTOSYNTHESIS
1. Set up the apparatus below twice over with the same amount of pondweed in each beaker.
2. Make sure that unlike the diagram, the test tube is full of water.
3. Put one plant in a sunny position and the other in a shady position.
4. After two days measure the length of test tube taken up by the oxygen produced.
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5. Gently pour out most of the water, keeping the test tube level. When most of it is poured out, keep your thumb on the top. You are trying to keep the oxygen in the test tube. It is a rather pesky gas and if you move the test tube too quickly it will escape.
6. Light a splint and put it out again. Dip the glowing splint into the gas in the test tube.
QUESTIONS
1. What did you notice about the gas produced after two days?
2. Did the gas test positive for oxygen?
3. What does this tell you about the amount of light in relation to photosynthesis?
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IMPORTANCE OF LIGHT WAVELENGTH IN PHOTOSYNTHESIS
Not all wavelengths of light are absorbed (used) by chlorophyll.
This can be shown by projecting a beam of light through a solution of chlorophyll extract and then through a prism to separate it into its different wavelengths.
After passing through a prism the light is projected on to a screen. Any colours absent from the spectrum are those that have been absorbed by the chlorophyll.
When doing this test in real life it is shown that the blue and red colours disappear from the spectrum. This means that the
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Light fromChlorophyllSolution
chlorophyll must absorb these colours.
The middle part of the spectrum, the green bit is not absorbed at all. Most of it is reflected, which is why leaves containing chlorophyll look green.
If different coloured lights are shined on plants, it is also found that red and blue lights increase the rate of photosynthesis the most.EXPERIMENT TO SHOW THAT CO2 IS NEEDED FOR PHOTOSYNTHESIS
1. Set up the equipment as shown below.
2. Add 20mL of 2 mol L-1 KOH to one of the conical flasks. This absorbs any CO2 left in the flask.
3. Add 20 mol L-1 H2CO3 to the other conical flask. This produces CO2.4. Make sure you label which flask is which.5. Seal the corks and any gaps with petroleum jelly.6. After a day carefully extract the leaves and test for starch.
QUESTIONS1. Why did you seal all gaps with petroleum jelly?
2. Why did you put a leaf in a flask with H2CO3 solution?
3. Discuss how this showed that the leaf with no CO2 did not photosynthesise?
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H2CO3 solutionGives off CO2
EXPERIMENT TO SHOW HOW VARYING THE AMOUNT OF CHLOROPHYLL CAN AFFECT THE RATE OF PHOTOSYNTHESIS
1. Chose a variegated leaf to test. Sketch or take a photo of (and paste into the results section) it, showing the different shades of green.
2. Place a variegated leaf / plant in the dark for at least 24h.3. Test for starch.4. Sketch or take a photo of (and paste into the results section) it, showing the
different shades of black, where the iodine has shown starch present.
QUESTIONS
1. Does a darker green show more or less chlorophyll to be present?
2. Does darker iodine staining show more or less starch to be present?
3. Write a conclusion for your experiment here.
Leaf before test Leaf after test
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EXPERIMENT TO SHOW HOW TEMPERATURE AFFECTS THE RATE OF PHOTOSYNTHESIS
1. Set up the apparatus below twice over with the same amount of pondweed in each beaker.
2. Make sure that unlike the diagram, the test tube is full of water.
3. Put both plants under a light for two days, but put one beaker on a heat mat.
4. After two days measure the length of test tube taken up by the oxygen produced.
QUESTIONS
1. What did you notice about the gas produced after two days?
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2. What does this tell you about the temperature in relation to photosynthesis?
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PHOTOSYNTHESIS SUMMARY
Using pages 49-56 from this workbook, summarise how photosynthesis is affected by different variables.
Complete the table.
Variable How is it changed? What happens to photosynthesis process?Light Removed
Light Intensity Decreased
Light Wavelength
In the green region
CO2 Levels Reduced
Chlorophyll Levels
Increased
Temperature Increased
If you’ve filled this table in correctly, it is very, very important that you know its contents.
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STRUCTURE OF THE LEAF
In a plant there are many different kinds of cells, each carrying out a different function. Groups of similar cells working together to do a similar job are called tissues. Different tissues work together to form an organ.
A leaf is a plant organ and within in it are many tissues each with a different role to play in a plants life processes. The leaf’s main function is to carry out photosynthesis.
MATCH THE NUMBERS ABOVE IN THE DIAGRAM TO THEIR DESCRIPTIONS BELOW.
Upper Epidermis - Consisting of epidermal cells. These have no chloroplasts.
Waxy Cuticle - Forms a waterproof layer to stop any loss of water.
Spongy Mesophyll Layer
Palisade cells - These contain lots of chloroplasts, which contain lot of chlorophyll. This is where photosynthesis is carried out.
Leaf Vein - containing xylem and phloem tubes.
Air Spaces - allow for diffusion of water vapour etc...
Guard Cells - These form stomata (pores) which allow for the diffusion of gases in and out of the plant.
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STRUCTURE OF THE LEAF – THE FOOD FACTORY
The leaf is the main site of photosynthesis. It has many adaptations which make it very efficient at this process.
Arrangement of leaves The leaves are arranged so that each individual leaf gains maximum sunlight. Look underneath a tree, not much light gets through.
Large surface area The large flat surface is the most efficient shape for absorbing the raw materials required for photosynthesis. i.e. sunlight and carbon dioxide.
Very Thin Most leaves are less than 1mm thick. This means that the gases required and produced by photosynthesis do not have as far to travel.
Pores There are pores on the underside of the leaf. These control entry and exit of gases and water from the leaf.
STOMATA
Stomata are the pores on the underside of a leaf. They allow carbon dioxide to enter a leaf and also control how much water the plant loses.
Guard cells control the opening and closing of the stomata. The stomata are normally open during the day as this is when photosynthesis is at its peak. During this time it needs the most carbon dioxide.
Unfortunately the features that make the leaf so good at absorbing CO2, also make it really good at losing water. Water diffuses out from the high concentration inside the leaf to the lower concentration outside the leaf. This loss of water is called transpiration.
On a warm sunny day a plant loses water over a hundred times faster than it uses water in the photosynthesis process.
When the soil is moist the roots are generally able to supply water as fast as the leaves lose it. When conditions are dry, water loss is a problem. The epidermis is the tissue responsible for dealing with water loss.
The upper epidermis secretes a waxy cuticle, which resists water loss
The lower epidermis contains many stomata which are surrounded by the guard cells. When the guard cells contain enough water they bend and open. When they become dehydrated
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they straighten and close the stoma. Thus it can be seen that in severe drought, photosynthesis would have to stop, as no more CO2 would be able to enter the leaf. This is why plants in dry conditions grow much slower. They are unable to produce the energy required to grow at a fast rate.
Look at this diagram of a leaf section. On the next page is a photo of a leaf section. Use the information on this page, to label the photo.
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CO2 ABSORPTION
Photosynthesis uses up CO2. As the CO2 within the leaf is used up by this process, the concentration inside the leaf decreases. This means that there is a greater concentration of CO2 outside the leaf. Fresh CO2 is thus able to diffuse in.
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WATER AND SUGAR TRANSPORTThe vascular bundles in a leaf contain the transport system of the plant. The xylem tubes deliver water. The phloem cells transport sugar from the leaf.
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