The Structure of the Leaf and the Process of

Photosynthesis

Unit 5- Part 1

Mrs. Stahl

Leaves • Major site of photosynthesis / food production.

• Minimize water loss by collecting water and transpiring.

• Transpiration is the process in which plants release water vapor through the pores of the skin or the stomata.

• Take in carbon dioxide and produce oxygen through the stomata.

• Stomata are tiny pores in the leaf.

• Protects stems and roots with shade and shelter.

Basic Structure • Blade- broad part of a leaf where most of the

photosynthesis of a plant takes place.

• Stipule- small leaf-like appendages.

• Petiole- stalk that attaches a leaf blade to a stem.

Organs of a Plant

Plant Organs

• Roots- anchors the plant. • Root Hairs- increase the surface area, allowing the

plant to absorb more nutrients and water. • Root tips- as plant roots grow, the cells in their tips

undergo constant mitosis to produce new tissue. • Stem- supports the plant so that it can “stand up.” The

protein lignin is found in the cell walls- makes the stem strong / supportive.

• Flower-reproductive structures of flowering plants (see foldable).

• Fruit- mature ovary of a flower. • Cone- reproductive structure of most gymnosperms

(pine trees / Christmas trees)

Roots and Root Hairs

Roots

Specialized Stems

• Cactus- photosynthesizes and stores water.

• Potato- grows underground

• Strawberry- form new plants by runners or stolons.

Plant Classification Plant Group Characteristics Common Example

Seedless nonvascular plants

Must grow close to the ground to absorb water and nutrients.

Liverworts Hornworts Mosses

Seedless vascular plants

Depend on water for reproduction, but a vascular system allows them to grow up off the ground.

Ferns Club mosses

Cone bearing seed plants

Gymnosperms- seed plant whose seeds are not enclosed in a fruit.

Cycads Ginkgoes Conifers

Flowering seed plants

Angiosperms- seed plant whose seeds are enclosed in fruit.

Flowering plants

Practice Question

• What is the main function of leaves?

– A. Leaves provide support for growth and a place to store food.

– B. Leaves provide a place for photosynthesis to occur.

– C. Leaves absorb water and minerals and transport nutrients to the stem.

– D. Leaves create a barrier that prevents water in the plant's tissues from evaporating.

Practice Question

• Plant cells that are specialized for cell division are most likely found in what part of the plant?

– A. root tips

– B. leaf epidermis

– C. stem epidermis

– D. vascular tissue

4 Types of Plant Tissues

• 1. Ground Tissue- most common

• 2. Dermal Tissue

• 3. Vascular Tissue

• 4. Meristematic Tissue- division of new cells.

Covers the outside - skin Live parenchymal cells cover the outside, and have a cuticle (guard cells) Bark= dead cells

Makes up much of the inside. Provides support and stores materials in roots and stems. Packed with chloroplasts.

Transport water, mineral nutrients, and organic compounds to all parts of the plant. Xylem and phloem.

Plants have specialized cells and tissue

systems.

Ground Tissue most common and they differ

based on their cell walls- 3 Types

–1. Parenchyma

–2. Collenchyma

–3. Sclerenchyma

• The most common plant cell

• Stores starch, oils, and water

• Helps heal wounds to the plant

• Found throughout the plant

• Ex- the flesh of many fruits we eat

Parenchyma Cells

–Provide support to a growing plant

–Strong and flexible.

–Unevenly thick cell walls.

–Ex- celery strings

Collenchyma Cells

–Strongest, supportive, and very thick cell walls

–Second cell wall hardened by lignin

–Die when they reach maturity

–Used by humans to make linen and rope

Sclerenchyma cells

Meristematic Tissue

• Growth tissue

• Where cell division occurs (root tips)

• Turns into ground, dermal, or vascular

• Apical meristems- tips of roots and stems-> primary growth occurs here.

• Lateral meristems- secondary growth. Increase the thickness of roots and stems. Think lat is fat.

stem

leaf

root

Leaf Structure Let’s go inside!!!

Use your foldable of the leaf and the chloroplast for this portion of the

notes.

• 1. Cuticle: waxy coating, prevents water loss, decreases microbial penetration, and the amount of wax increases with light intensity exposure.

• 2. Upper Epidermis: no chloroplasts; provides a clear passageway for light to penetrate into the leaf.

• 3. Palisade Mesophyll: Filled with chloroplasts; performs more photosynthesis because it is closer to the top of the leaf.

• 4. Spongy Mesophyll: Contain chloroplasts and performs photosynthesis. Not as efficient as the palisade mesophyll.

• 5. Air Spaces: allow gases to be exchanged between the inside and outside of the leaf. Oxygen exits, CO2 enters.

• 6. Lower Epidermis: coats the bottom of the leaf (cuticle). Contains stomata for gas exchange. More stomata at the bottom of the leaf than at the top.

• 7. Stoma: allows for gas exchange. The opening and closing is regulated by guard cells.

• 8. Guard cells: help form the stoma. Inflate to open the stoma, or deflate to close the stoma.

• 9. Vascular Bundle (Vein): xylem & phloem surrounded by the bundle sheath. Passageways in the leaf, stem, and root of the plant.

• 10. Bundle Sheath Cells: surround the xylem and phloem, strengthen the veins, and protect the conductive tissues.

• 11. Xylem: transports water and minerals from the roots to the leaves.

• 12. Phloem: “food,” transports glucose and other products from the leaf to other parts of the plant for use or storage. Ex- sap.

The Chloroplast Diagram

• 13. Outer Membrane: semi-permeable, smooth, phospholipid membrane.

• 14. Inner Membrane: semi- permeable, phospholipid bilayer under the outer membrane.

• 15. Intermembrane Space: region between the outer and inner membranes.

• 16. Stroma: liquid in the inner chloroplast. Contains enzymes needed to catalyze the LDR (light dependent reactions) in photosynthesis.

• 17. Granum: “stack of pancakes,” stack of thylakoids

• 18. Thylakoid: houses the chlorophyll (pigment), which helps with photosynthesis. Light absorption (LDR). Contains accessory pigments, enzymes, and electron transport systems.

• 19. Thylakoid Lumen: the region located within each thylkoid.

• 20. Lamella: connect two or more grana to each other. Makes sure the grana are evenly spaced to maximize the ability to intercept sunlight.

How fluids move through the xylem

• See handout of slides.

Water and dissolved minerals move through xylem.

• Xylem contains specialized cells. – vessel elements are short and wide

– tracheid cells are long and narrow

– xylem cells die at maturity

vessel element

tracheid

– Plants passively transport water through the xylem.

– Cohesion is the tendency of water molecules to bond with each other.

The cohesion-tension theory explains water movement.

– Adhesion is the tendency of water molecules to bond with other substances.

– absorption occurs at roots

Water travels from roots to the top of trees

– cohesion and adhesion in xylem – transpiration at leaves

– water vapor exits leaf stomata

– helps pull water to the top branches

Transpiration is the loss of water vapor through leaves.

Phloem carries sugars from photosynthesis throughout the plant.

• Phloem contains specialized cells. – sieve tube elements have holes

at ends – companion cells help sieve

tube elements – unlike xylem, phloem tissue is

alive

– plants actively transport sugar from the source

– sugar flows to the sink due to pressure differences

sugars

phloem xylem

water

Sugars move from their source, such as photosynthesizing leaves, into the phloem.

1

The sugars move into the sink, such as root or fruit, where the are stored. 3

Water moves from the xylem into the phloem by osmosis, due to the higher concentration of the sugars in the phloem. The water flow helps move sugars through the phloem.

2

The Pressure-flow model explains sugar movement.

• http://www.classzone.com/cz/books/bio_12_fl/resources/htmls/animated_biology/unit7/bio_ch21_0644_ab_material.html

Cambium

• Plant tissue from which phloem, xylem, or cork grows by division, resulting (in woody plants) in secondary thickening.

The Importance of Guard Cells and Stomata

• The stoma is the site of transpiration and gas exchange.

• Guard cells surround each stoma, and open and close by changing shape.

• Day- stoma is open, allowing the carbon dioxide to enter and water to evaporate.

• Night- close

• Why do they close at night?

Answer

• During the day, photosynthesis requires that the leaf mesophyll be exposed to the air to get CO2. At night, the stomata close to avoid losing water when photosynthesis is not occurring. During the day, stomata close if the leaves experience a lack of water, such as during a drought.

Guard Cells Open Stoma

• Allows CO2 necessary for photosynthesis to enter.

• Open due to potassium ions from neighboring cells accumulating in the guard cells, causing water to also enter the guard cells.

• Water evaporates from the leaves.

• Potassium ions accumulate in the guard cells and when there is a high concentration of K+ it causes water to flow into the cells. When the plant is full of water, the guard cells plump up and open the stomata.

Closed Stoma • When the plant is losing water

from leaves faster than it is gaining water at its roots, the guard cells deflate and close their stomata.

• May run low on CO2 and slow or stop photosynthesis.

• Stomata close at night.

Factors that cause the guard cells to open and close

• Temperature

• Humidity

• Hormones

• Amount of carbon dioxide in the leaves tells the guard cells to open and close.

Practice Question • Terrestrial plants have stomata on the surface of their

leaves. A single stomata is surrounded by two guard cells that change shape in response to environmental factors and open or close the stoma. Which of the following best explains how the structure of the leaf is used in processes that occur in plants? – A. Water enters the plant through the surface of the leaf for

transpiration – B. Gases for photosynthesis are exchanged through the surface

of the leaf. – C. Energy for cellular reproduction is absorbed through the

surface of the leaf. – D. Carbon dioxide enters the plant through the surface of the leaf

for cellular reproduction.

Practice Question

• If the xylem in a young tree is damaged, which process is first affected?

– A. performing photosynthesis

– B. transporting sugar to the roots

– C. transporting water to the leaves

– D. absorbing water from the soil

Practice Question

• A plant species lives in an area with limited sunlight. Which physiological adaptation would be most useful to the plant?

– A. colorful flowers

– B. large leaves

– C. deep roots

– D. thin cuticle

Practice Question

• The cambium is a section of cells in a plant that can become either part of the xylem or phloem, depending on the growth and needs of the plant. If the cambium of a particular plant was damaged, what would be the most likely effect on the plant?

• A. The plant would lose its ability to carry out photosynthesis.

• B. the plant would have uncontrolled growth. • C. The plant would not experience any change in

physiology. • D. The plant would not be able to transport nutrients and

water.

Practice Question

• Which structure in the leaf controls the opening and closing of the stoma?

• A. cuticle

• B. epidermis

• C. guard cell

• D. spongy mesophyll

Practice Question • The diagram below shows a cross section of a plant leaf.

• How does the structure marked X contribute to the survival of the plant?

• A. It allows the intake of gases necessary for photosynthesis. • B. It allows the intake of minerals necessary for plant growth. • C. It allows the intake of sunlight necessary for ATP production. • D. It allows the intake of sugars necessary for plant reproduction.

Plant Reproduction

Plant life cycles alternate between producing spores and gametes.

• A two-phase life cycle is called alternation of generations. – haploid phase

(single set of chromosomes).

– diploid phase (two complete sets of chromosomes).

– alternates between the two

fertilization

meiosis

SPOROPHYTE PHASE

GAMETOPHYTE PHASE

–sporophyte phase is diploid –begins with fertilized egg –spores produced through

meiosis

• The gamete-producing plant is the mature gametophyte.

The spore-producing plant is the mature sporophyte.

– gametophyte phase is haploid – begins with spore – gametes produced through mitosis

• The sporophyte is the dominant phase for seed plants.

Review

Angiosperms- Flowering plants

• See foldable

What to Color

Definitions for foldable 1. Pistil- All of the female reproductive structures: stigma,

style, ovary, ovules. 2. Stigma- Tip of the pistil & it is “sticky” - pollen sticks to it.

The moisture on the stigma helps rehydrate pollen. Can discriminate between good and bad pollen.

3. Style- Connects the stigma to the ovary. Tall to make sure that pollination can occur.

4. Ovule- Produces female gametes- egg cells. When fertilized it will turn into the seed of a fruit (the seed is the embryo of the plant).

5. Ovary- Houses and protects the ovules. When eggs are fertilized by pollen, the ovary transforms into the fleshy part of the fruit, which will house and protect the seeds.

6. Peduncle- Stalk holding up the flower. It becomes the stem that is found attached to some fruit.

7. Receptacle- Thick part of the stem from which the flower structures grow. In some plants it helps fruit along with the ovary.

8. Petal- Protects reproductive structures. Attracts pollinators. Repel/deter predators.

9. Pollen Grains- Male Gametes (sperm cells)

10. Anther- Located at the ends of filaments and produces the pollen grains.

11. Filament - Stalk that holds up the anther. Very long, located higher than the stigma.

12. Stamen- includes all of the male reproductive organs of a flower. -Filament -Anther -Pollen grains

13. Sepal- small leaves at the base of the flower. Initially they enclose the flower bud and protect it. When the flower blossoms, they serve to support the base of the flower.

Pollination

● Necessary for sexual reproduction to occur in plants.

● Occurs via insects, wind, rain, and feces.

Asexual Reproduction

● Regeneration- plants that can grow a new individual from a fragment of a stem, leaf, or root.

● Ex- prickle pear

● Vegetative reproduction- type of asexual reproduction in which stems, leaves, or roots attached to the parent plant produce new individuals.

● Ex- Aspen trees in Utah- covers 100 football fields and the forest is 47,000 trunks growing from one parent plant.

Physiological Process of Transpiration,

Photosynthesis, and Cellular Respiration

Transpiration

• Evaporation of water from leaves.

• Water is pushed up through the xylem by root pressure created from water moving up the soil to the plants root system and into the xylem-> results in small droplets of sap-> called guttation.

• Water is also pulled up through cohesion through the xylem tissue-> creates a negative pressure or tension from roots to leaves.

Rate of Transpiration

• Slows in high humidity

• Accelerates or speeds up in low humidity

• Increases with wind

• Increases with intense light= increased photosynthesis and water vapor

Photosynthesis

• Defined as the process that captures energy from sunlight to make sugars that store chemical energy.

• Location- Chloroplast of plant cells.

Chloroplast

Leaf Cell

Leaf

Photosynthesis • Chloro= Green

• Phyll= Leaf

• Plast = Molded

chloroplast

leaf cell

leaf

Two Processes

• Light dependent reactions= NEED SUNLIGHT

• Light independent reactions= OCCUR IN THE DARK

Equation

Chloroplast- refer to your foldable

• Three main parts are:

–Grana- stacks of coined shaped membranes.

Thylakoid – Inside the grana and they are the little disks.

They contain chlorophyll and other light absorbing pigments.

– Photosystems- light collecting units. They are proteins that organize chlorophyll and other pigments into clusters.

Add this onto your foldable.

Stroma

– Fluid that surrounds the grana inside the chloroplast.

• Chlorophyll- the molecule in the chloroplast that absorbs the energy from the sunlight. There are two main types, chlorophyll a and b, that absorb mostly red and blue light. Other pigments absorb the green.

• Green color in plants comes from the reflection of the green wavelengths by chlorophyll.

Carotenoids are yellow-orange pigments which absorb light in violet, blue, and green regions.

When chlorophyll breaks down in fall, the yellow-orange pigments in leaves show through.

You do not

have to put

this in your

notes!!!

Just a little

fun fact!

Fall Foliage

So let’s begin

• The sunlight hits the leaves and CO2 is let in through the stoma (little pores), while H2O is let in through the roots.

Light Dependent Reactions or Light

Reactions – Requires sunlight

– Take place in the thylakoids

– Water and sunlight are needed

– Chlorophyll absorbs energy

– Energy is transferred along the thylakoid membrane and then to light-independent reactions

– Oxygen is released as a waste product

Photosynthesis is broken down into two different reactions!!!

1st

Light Dependent Cont.

• Electron Transport Chain (ETC)- series of proteins in the membrane of the thylakoid.

• Energy-> electrons->ATP and NADPH (transferred to the later stages)

• Arrows represent energy and enzymes!

• NADP= coenzyme that can accept hydrogen and acts as an enzyme

http://www.biology-online.org/dictionary/Nicotinamide_adenine_dinucleotide_phosphate

Light Independent Reactions

• Uses the energy transferred from the light dependent reactions to make sugars.

• Reactions occur in the stroma

• Does NOT require sunlight

• Carbon dioxide is absorbed and used at this stage.

• Calvin Cycle- metabolic pathway found in the stroma of the chloroplast; where carbon enters in the form of CO2, and leaves in the form of glucose.

• ATP is produced as a final step. The enzyme ATP synthase is responsible for making ATP by adding phosphate groups to ADP.

2nd

Light Independent / Calvin Cycle

• Energy sources are ATP and NADPH

• Energy that is needed for a series of chemical reaction is called the Calvin Cycle, named after the scientist- Melvin Calvin.

• Rubisco is the enzyme used to set up the Calvin Cycle. It’s said to be the most abundant protein on Earth, but is much slower than most enzymes.

Chloroplast

CO2 from the atmosphere

Energy carrying molecules transferred to the LIR

Glucose

Oxygen

Thylakoid

Sunlight entering

Calvin Cycle in the stroma

Chlorophyll

H2O

ATP & NADPH

Energy is transferred to electrons

Questions to review

• 1. Where do the light dependent reactions occur?

• 2. Where do the light independent reactions occur?

• 3. What two reactants are shown entering the chloroplast?

• 4. What two products are shown leaving the chloroplast?

• 5. What does the Calvin Cycle produce?

Answers

• 1. Thylakoid membrane

• 2. Stroma

• 3. Water and carbon dioxide

• 4. Oxygen and sugar

• 5. Glucose

A detailed perspective

Light Dependent Reactions • 1. Energy absorbed from sunlight is transferred to electrons

(electrons = energy) that enter the ETC. • 2. Water molecules are broken down; electrons enter

chlorophyll. • 3. Electrons jump from protein to protein down the ETC, and

their energy is used to pump the H+ ions from outside to inside the thylakoid membrane (against the concentration gradient = ACTIVE TRANSPORT)

• 4. Energy from sunlight continues to be absorbed, energizing electrons and pushing them along the ETC.

• 5. Electrons are then added to the molecule NADP+ (functions like ADP) to produce NADPH (functions like ATP).

• 6. H+ ions flow (diffusion) through a channel in the thylakoid membrane.

• 7. ATP is produced. ADP is changed into ATP when hydrogen ions flow through ATP synthase (enzyme).

Photosystem II captures and transfers energy.

Photosystem I captures energy and produces energy-carrying molecules.

Light Independent Reactions

• 1. Carbon dioxide enters the Calvin Cycle, and are added to the already five carbons molecules that are there.

• 2. Energy is added. The six carbon molecules split to form three- carbon molecules. More energy is added (ATP & NADPH), and the molecules are rearranged into higher energy molecules.

• 3. A high energy three-carbon molecule exits for every 3 CO2 molecules that enter. After 2 three-carbon molecules have exited, they bond to form 1 six-carbon sugar.

• 4. Three carbon-molecules are changed back to five carbon molecules by energy from ATP.

Videos

https://vimeo.com/7316737 http://www.mhhe.com/biosci/bio_animations/02_MH_Photosynthesis_Web/ http://www.youtube.com/watch?v=lDwUVpOEoE4

Review Questions

• 1. Where do the light reactions occur?

• 2. Where do the electrons come from in the ETC?

• 3. What role do these electrons play?

• 4. What two energy carriers are produced?

• 5. When does active transport take place?

• 6. What enzyme speeds up the process?

• 7. Where in the chloroplast do light independent reactions occur?

• 8. Where do ATP and NADPH come from for the light independent reactions?

• 9. What does the LDR make? What does the LIR make?

• 10. How many cycles or turns does it take to make one glucose molecule?

• 11. What enzyme sets up the Calvin Cycle?

Answers • 1. Thylakoid membrane

• 2. Chlororphyll

• 3. Provide energy to move hydrogen ions into the thylakoid and to produce molecules of NADPH

• 4. NADPH and ATP

• 5. Step 3 when hydrogen ions are transported

• 6. ATP synthase

• 7. Stroma

• 8. LDR

• 9. LDR= makes ATP, LIR= makes sugars

• 10. 2

Let’s Summarize- Bellwork

Process Location Reactants Ending Products

Light Dependent Reactions Where the photosystems take place.

Light Independent Reactions. Where the Calvin Cycle takes place

Write the Equation for Photosynthesis

Let’s Summarize

Process Location Reactants Ending Products

Light Dependent Reactions Where the photosystems take place.

Thylakoid Membrane Sunlight H2O

ATP NADPH O2

Light Independent Reactions. Where the Calvin Cycle takes place

Stroma ATP NADPH CO2

Glucose

6CO2 + 6H2O -> C6H12O6 + 6O2