Plant structures and their functions

... organisms are the main .... of food and therefore ....

1. photosynthetic organisms

2. producers

3. biomass

What type of reaction is photosynthesis?

endothermic

What are the reactants and products of photosynthesis?

carbon dioxide + water ---> glucose + oxygen

what energy does photosynthesis use to convert CO2 and H2O into C6H12O6 and O2?

light energy

Explain the effect of temperature on the rate of photosynthesis

As temperature increases, so does the rate of photosynthesis because the enzymes gain more kinetic energy so more collisions take place.

Until past the optimum temperature when the enzymes denature

Explain the effect of carbon dioxide concentration on the rate of photosynthesis

as co2 concentration increases, so does the rate of PS because more raw material is available to convert into glucose

explain the effect of light intensity on the rate of photosynthesis

as light intensity increases, the rate of PS increases because there is more light energy to convert into chemical energy

What are the 3 components of photosynthesis that can limit the rate

If light intensity, temperature or CO2 concentration is in short supply, the rate of photosynthesis is limited

why does the graph plateau

a further increase in light intensity makes no difference because another factor is in short supply, limiting the rate

deduce from the graph the limiting factor in this experiment

temperature

Describe the CP used to investigate the effect of light intensity on the rate of photosynthesis

1. In a test tube place pondweed in water

2. top with a bung and gas syringe

3. record how far away the test tube is from the lamp and measure the volume of gas produced by the pondweed

4. repeat experiment at different distances from lamp

rate of photosynthesis is ..... proportional to light intensity

directly

rate of photosynthesis is ..... proportional to the distance from light source

inversely

Why is rate of PS directly proportional to light intensity

Becuase the greater intensity of light, the more photons (light energy) hit the chloroplasts in the leaf, and the more PS can occur at once

Why is the rate of PS inversely proportional to the distance from light source

Becuase as distance from light source increases, rate of PS decreases

Inverse square law

light intensity = 1/distance²

function of a root hair cell

To absorb water and mineral ions for the plant (via osmosis and active transport)

Explain root hair cell adaptations

1. large surface area to volume ratio so more water can move in by osmosis

2. large permanent vacuole keeps a steep concentration gradient so water can enter root hair cell quicker

3. lots of mitochondria to provide energy for active transport to take up mineral ions

function of xylem cells

To transport water and mineral ions from the roots to the leaves

Adaptation of xylem cells

lignified dead cells are hollow and are joined end-to-end to form a continuous tube so water and mineral ions can move through

Function of phloem cells

to carry the products of photosynthesis (sucrose) to all parts of the plant

Adaptation of phloem cells

cells are alive with lots of mitochondria in the companion cells to release energy to transport sucrose around the plant

Define transpiration

the evaporation of water vapour from the leaves and stems of plants due to the water potential gradient between the leaves and roots

Where does transpiration occur?

Through the stomata (pores) on primarily on the lower epidermis

What is the role of the stomata?

Stomata are tiny pores on the underside of the leaf, these control the gas exchange in the leaf. Each stoma can be opened or closed, depending on how turgid the guard cells are

How do the stomata operate?

Guard cells control the opening and closing of the stomata. The more water in the cell, the more turgid the guard cells become, opening the stomata more

How does light impact the opening and closing of the stomata?

The guard cells open the stomata in the light, because that's when photosynthesis occurs when water is needed, and close in the dark to save water

Why are most of the stomata on the underside of the leaf?

To retain more water because they are not directly in the sun so less evaporates from heat

How does the transpiration stream work?

1. water is lost at the leaves by transpiration

2. To replace the lost water, water is drawn out of the xylem into the leaves

3. Root hair cells draw in water from the soil by osmosis to replace water in xylem, resulting in a continuous transpiration stream

Define translocation

the movement of sucrose made in the leaves up or down the phloem, for use immediately or for storage

Where does translocation occur?

Phloem

Give 4 adaptations of the leaf for photosynthesis and gas exchange

Stomata: allow gas exchange and transpiration for photosynthesis

Chlorophyll: green- most efficient colour for absorbing light so as much light as possible is absorbed for photosynthesis

Thin leaves: means that oxygen and co2 only have a short diffusion pathway

Large surface area: leaf can absorb more light at once, maximising rate of photosynthesis

How does temperature affect the rate of transpiration?

Increase of temp=increased rate of transpiration

Because water is gaining kinetic energy from heat and evaporating faster

How does light intensity affect the rate of transpiration?

Increase of light intensity= increased rate of transpiration

Because the more intense the light, the wider the stomata so more water can diffuse outwards

How does wind speed affect the rate of transpiration?

Increased wind velocity= increased rate of transpiration

Because high wind speed moves saturated air away from the leaves, maintaining a high concentration gradient

How to calculate the rate of transpiration?

distance moved by bubble/time taken

Explain 3 adaptations of plants adapted to extreme conditions

No/small leaves: reduces amount of water lost as a result of transpiration

Waxy cuticle: prevents the evaporation of water in environments where water is scarce

Stomata: can adjust to conditions to prevent water loss

What is phototropism?

Response to light

What is gravitropism?

response to gravity

What does it mean if the tropism is positive?

Grows towards the stimulus

What does it mean if the tropism is negative?

Grows against the stimulus

What does it mean if plant shoots are positively phototrophic?

Means they grow towards the light- important for maximum light capture for photosynthesis

What is an auxin?

Growth hormone

How do auxins work in shoots?

When a plant is in the light, the shades side accumulates more auxin

The cells on the shaded side elongate so the shoot bends towards the light to maximise light capture for photosynthesis

This makes shoots positively phototropic

How do auxins work in roots?

Root growing sideways has more auxin on the lower side

In a root auxin inhibits growth so the top cells elongate, the root bends downwards

This makes roots positively gravitropic

Commercial uses of auxins

Weedkillers

Rooting powders

Commercial uses of gibberellins

Germination

Fruit and flower formation

Production of seedless fruit

Commercial uses of ethene

Fruit ripening