Pop-Quiz

What two gases must be regulated in the body?

List the five areas that hormones are responsible for in plants?

List the main groups of hormones

Answer Oxygen and Carbon dioxide must

be regulated in the body Hormones in plants are responsible

for phototropism, geotropism, apical dominance, ripening of fruit, abscission.

The main groups of hormones are Auxins, gibberellins, cytokinins, abscisic acid and Ethylene

So what and how do plants respond?

Plants have a number of stimuli to deal with in their environment:

Light is needed to photosynthesis Plants need to know when it is the

best time of year to flower Seeds need to know which way is

down so as to send roots and shoots in the right direction

Plant Tropisms 1. Tropism: the way a plant grows in response to

stimuli in the environment.Phototropism: growth response to light

-Plants bend towards light

Geotropism: growth response to gravity-plant roots grow down with gravity, shoots (stems) grow up against gravity and out of the soil.

Thigmotropism: growth response to touch-vines grow up around trees, venus flytrap closes when leaves are touched

Geotropism

What type of tropism is shown in these pictures?

Thigmotrophism

Thigmotrophism

Geotropism

Phototropism

Phototropism

light Phototropism in

growing shoots is a response to blue light.

Other responses are stimulated by different light Reponses.

Positive phototropism is the growth towards the light source.

Photoperiod and flowering Some plants

require long nights to flower others require short nights.

Photoperiod is the length of time to which an organism is exposed to light

Gravity Geotropism is the

response of plants to gravity.

Roots are positively geotropic they grow towards the pull of gravity

Touch Thigmotropism is

growth changes in response to contact with a surface

Movement response are produced by changes in the internal fluid pressure of particular groups of cells.

Tropism Stimulus Effect Response

Phototropism Light Cell elongation stimulated on the shade side of the plant

The growing shoot bends towards the light

Gravitropism or Geotropism

Gravity Cell elongation is stimulated on upper portion of root

The growing root bends towards the centre of gravity

Hydrotropism Water availability

Root tips closest to a water source & soluble minerals grow faster than those further away

Growth of the root towards a water source

Thigmotropism Touch Plant runners change direction when they come in contact with any object.

Plant runners (eg Vines) wrap around branches or trellis etc

Temperature Some plants enter a

dormant stage before winter; bud dormancy is broken by a period of winter cold. Seeds enter a dormant stage and remain so until conditions are right for successful germination.

Some plants require exposure to cold(vernalisation) as seeds, others require vernalisation after their first year of growth, in order to complete their life cycle.

Summary:Water and nutrients Most land plants

obtain water and nutrients from soil.

Most nutrients are taken up selectively by active transport into roots; Water moves into roots passively.

Summary:Transport of substances Most water and

nutrients pass through the root along cell walls; some pass through the cytoplasm of root cells.

Transport occurs in xylem or phloem

PHLOEM Sucrose (food) is

transported by the vascular tissue called phloem. Unlike transpiration's one-way flow of water sap, food & hormones in phloem sap can be transported in any direction needed.

Phloem The bulk-flow mechanism translocates sap from

sugar sources to sugar sinks in the plant. Phloem sap is mainly water and sucrose, but other sugars, hormones and amino acids are also transported. The movement of such substances in the plant is called translocation. Translocation means the transportation of photosynthetically produced food throughout the entire body of the plant through the phloem cells. Another mechanism that induces the flow or movement of sap through the phloem of a plant is the transpiration-condensation-tension mechanism.

Xylem Bulk flow of xylem

sap (water and nutrients ions) from roots to leaves occurs within xylem vessels and tracheids.

It is driven by transpiration and root pressure

Transpiration/ Root pressure Transpiration is

the loss of water vapour from leaves. The rate of transpiration depends on factors that affect the rate of evaporation: temperature, wind, available surface area and humidity.

Fluid pressure generated by the osmotic uptake of water accompanying the active uptake of mineral salts into roots contributes to the movement of water up the xylem in plants.

Stomata Stomatal movement

is the result of changes in the internal fluid pressure of the guard cells in response to environmental conditions light, carbon dioxide and water in particular

What causes STOMATAL opening

The immediate cause is an increase in turgor pressure - water enters the central vacuole by osmosis

Turgor pressure increases because of a negative water potential due to an influx of potassium ions (K+). The cell becomes hypertonic to its environment

The reversible uptake of K+ ions takes place because of the membrane potential created when H+ are actively pumped out of the cell - consuming ATP. The cell's interior becomes negative compared to the surroundings.

Regulating Stomata

The stoma is closed at night when the large central The stoma is closed at night when the large central vacuole is isotonic, even hypotonic to surrounding vacuole is isotonic, even hypotonic to surrounding fluids. K+ ions are outside of the cell, and H+ ions by fluids. K+ ions are outside of the cell, and H+ ions by and large remain attached to the weak organic acids and large remain attached to the weak organic acids within the cell.within the cell.Blue light is absorbed by a membrane protein which Blue light is absorbed by a membrane protein which somehow causes an increase in the activity of proton somehow causes an increase in the activity of proton pumps which use ATP to transport H+ out of the cell.pumps which use ATP to transport H+ out of the cell.With H+ on the outside K+ readily diffuse into the cell With H+ on the outside K+ readily diffuse into the cell to compensate for the negative electrical potential. The to compensate for the negative electrical potential. The hypertonic conditions within the cell attract water hypertonic conditions within the cell attract water molecules and the stoma opens as turgor pressure molecules and the stoma opens as turgor pressure increases.increases.

A cell in a hypertonic environment is surrounded by a higher concentration of impermeable solute than exists in the inside of the cell. Osmotic pressure directs a net movement of water out of the cell, causing it to shrink.

The opposite of a hypertonic environment is a hypotonic one, where the net movement of water is into the cell. If the cell contains more impermeable solute than its surroundings, water will enter it. In the case of animal cells, they will swell until they burst; plant cells do not burst, due to the reinforcement their cell wall provides.

Internal Environment of Plants In plants the

distinction between extracellular fluid and the external environment is less clear than it is in animals and the composition of extracellular fluids is not regulated as precisely

Movement in/out of leaves

During daylight, plants are performing photosynthesis at a greater rate than cellular

respiration (if STOMATA are open.)•A - C/R is at constant rate

•B – photosynthesis is unable to occur or limited by light (night)

•C – compensation point

•D - light intensity high (enzymes working at max. level)

Summary

Plants need to respond to their external environment including light, gravity, touch, day length and temperature.

Plants also need to transport materials such as water and nutrients around the plants structure they use the xylem for water and phloem for nutrients