Plant structures and their functions
explain photosynthesis
● occurs in photosynthetic organisms, such as green plants and algae, which are the main
producers of food and biomass
● endothermic reaction that uses light energy to react carbon dioxide and water to produce
glucose and oxygen
How does light intensity affect the rate of photosynthesis?
Light transfers the energy needed for photosynthesis so when the light level is raised, the rate of
photosynthesis increases. But this is only true up to a certain point
How does carbon dioxide concentration affect the rate of photosynthesis?
CO2 is needed for photosynthesis so when the CO2 concentration increases, the rate of
photosynthesis also increases but up to a certain point
How does temperature affect the rate of photosynthesis?
When temperature increases the rate of photosynthesis also increases. however if its too hot
the enzymes it needs will denature
How can you measure the effect of light intensity on the rate of photosynthesis? (core practical)
● use the ruler to place flask and pondweed a certain distance from the lamp. Connect the
gas syringe to the flask
● leave apparatus for a set amount of time so the pondweed can photosynthesise
● oxygen released will collect in the gas syringe so you can measure the volume of oxygen
produced
explain the inverse square law
rate of photosynthesis is directly proportional to light intensity and inversely proportional to the
distance from a light source
inverse square law calculation:
light intensity = 1/ (distance)^2
How are root hair cells adapted to absorb water and mineral ions?
● the cells on the surface of plant roots grow into hairs which give the plant a large surface
area for absorbing water and mineral ions from the soil
● the concentration of mineral ions is higher in root hair cells than in the soil so mineral
ions are absorbed by active transport, while water is absorbed by osmosis
How is a phloem cell adapted for its function?
, ● made out of columns of elongated living cells with small pores in the end walls so stuff
can flow through
● they transport food substances (mainly sucrose) made in the leaves to the rest of the
plant for immediate use or storage, which is called translocation and requires energy
from respiration and goes in both directions
How are xylem adapted to their function?
● made from dead cells joined with no end walls and strengthened with lignin
● they carry water and mineral ions from the roots to the stem and leaves
explain transpiration
● transpiration is the movement of water from the roots, through the xylem and out of the
leaves
● caused by the evaporation and diffusion of water from a plant's surface, which creates a
loss of water. This means that more water is drawn through the xylem vessels to replace
it
explain the structure and function of the stomata
● stomata are tiny pores on the surface of a plant
● they allow CO2 and oxygen to diffuse in and out of a leaf, and water vapour to escape in
transpiration
● they are surrounded by guard cells which change shape to control the size of the pore
● When the guard cells are swollen with water, the stomata are open. When the guard
cells are low on water/limp, the stomata are closed
How does light intensity affect the rate of transpiration?
the higher the light intensity, the higher the rate of transpiration. this is because stomata close
when its dark so very little water can escape for transpiration
How does temperature affect the rate of transpiration?
The higher the temperature, the higher the rate of transpiration. This is because at high
temperatures, water particles have more energy to evaporate and diffuse out of the stomata
How does air movement affect the rate of transpiration?
the higher the air movement, the higher the rate of transpiration. This is because if there is more
air movement, water vapour is swept away, maintaining a low concentration of water in the air
outside the leaf, so diffusion can happen quickly
How are leaves adapted for efficient photosynthesis and gas exchange?
● leaves are broad, so there is a large surface area that is exposed to light, which is
needed for photosynthesis, and lots of chloroplasts
, ● the upper epidermis is transparent so light can pass through it to get to the palisade
layer
● the epidermal tissues are covered with a waxy cuticle so they can reduce the water lost
by transpiration
How are plants adapted to live in extreme environments?
● small leaves to reduce the surface area for water loss by evaporation
● hairs on the surface trap water vapour, reducing diffusion from the leaf to the air
● thick waxy cuticles to reduce water loss by evaporation
● fewer stomata/stomata that only open at night to reduce water loss by evaporation
● stomata in small pits which reduces air flow close to the stomata, reducing water loss
How can you estimate the rate of transpiration?
using a potometer. The air bubble moves along the tube as the plant loses water. The speed of
the bubble gives a measure of the rate of transpiration
explain the role of auxins in the growth responses of shoots to light
● shoots grow towards the light (positively phototropic)
● when the tip of the shoot is exposed to light, auxins move to the shaded side of the
shoot
● this makes the cells grow faster on the shaded side, so the shoot bends towards the light
explain the role of auxins in the growth responses of shoots to gravity
● shoots grow away from gravity (negatively gravitropic)
● when a shoot is growing sideways, auxins are pulled downwards by gravity, increasing
cell elongation so the shoot grows upwards
explain the role of auxins in growth responses of roots to light
● roots grow away from light (negatively phototropic)
● if a root is exposed to light, auxins move to the shaded side of the root
● the auxin inhibits cell elongation on the shaded side so the root bends downwards
explain the role of auxins in growth responses of roots to gravity
● roots grow towards gravity (positively gravitropic)
● when a root grows sideways, auxins are pulled downwards by gravity and inhibit cell
elongation so the root grows downwards
describe the commercial uses of auxins
● auxins are in selective weedkillers to kill plants that have broad leaves but not narrow
leaves
explain photosynthesis
● occurs in photosynthetic organisms, such as green plants and algae, which are the main
producers of food and biomass
● endothermic reaction that uses light energy to react carbon dioxide and water to produce
glucose and oxygen
How does light intensity affect the rate of photosynthesis?
Light transfers the energy needed for photosynthesis so when the light level is raised, the rate of
photosynthesis increases. But this is only true up to a certain point
How does carbon dioxide concentration affect the rate of photosynthesis?
CO2 is needed for photosynthesis so when the CO2 concentration increases, the rate of
photosynthesis also increases but up to a certain point
How does temperature affect the rate of photosynthesis?
When temperature increases the rate of photosynthesis also increases. however if its too hot
the enzymes it needs will denature
How can you measure the effect of light intensity on the rate of photosynthesis? (core practical)
● use the ruler to place flask and pondweed a certain distance from the lamp. Connect the
gas syringe to the flask
● leave apparatus for a set amount of time so the pondweed can photosynthesise
● oxygen released will collect in the gas syringe so you can measure the volume of oxygen
produced
explain the inverse square law
rate of photosynthesis is directly proportional to light intensity and inversely proportional to the
distance from a light source
inverse square law calculation:
light intensity = 1/ (distance)^2
How are root hair cells adapted to absorb water and mineral ions?
● the cells on the surface of plant roots grow into hairs which give the plant a large surface
area for absorbing water and mineral ions from the soil
● the concentration of mineral ions is higher in root hair cells than in the soil so mineral
ions are absorbed by active transport, while water is absorbed by osmosis
How is a phloem cell adapted for its function?
, ● made out of columns of elongated living cells with small pores in the end walls so stuff
can flow through
● they transport food substances (mainly sucrose) made in the leaves to the rest of the
plant for immediate use or storage, which is called translocation and requires energy
from respiration and goes in both directions
How are xylem adapted to their function?
● made from dead cells joined with no end walls and strengthened with lignin
● they carry water and mineral ions from the roots to the stem and leaves
explain transpiration
● transpiration is the movement of water from the roots, through the xylem and out of the
leaves
● caused by the evaporation and diffusion of water from a plant's surface, which creates a
loss of water. This means that more water is drawn through the xylem vessels to replace
it
explain the structure and function of the stomata
● stomata are tiny pores on the surface of a plant
● they allow CO2 and oxygen to diffuse in and out of a leaf, and water vapour to escape in
transpiration
● they are surrounded by guard cells which change shape to control the size of the pore
● When the guard cells are swollen with water, the stomata are open. When the guard
cells are low on water/limp, the stomata are closed
How does light intensity affect the rate of transpiration?
the higher the light intensity, the higher the rate of transpiration. this is because stomata close
when its dark so very little water can escape for transpiration
How does temperature affect the rate of transpiration?
The higher the temperature, the higher the rate of transpiration. This is because at high
temperatures, water particles have more energy to evaporate and diffuse out of the stomata
How does air movement affect the rate of transpiration?
the higher the air movement, the higher the rate of transpiration. This is because if there is more
air movement, water vapour is swept away, maintaining a low concentration of water in the air
outside the leaf, so diffusion can happen quickly
How are leaves adapted for efficient photosynthesis and gas exchange?
● leaves are broad, so there is a large surface area that is exposed to light, which is
needed for photosynthesis, and lots of chloroplasts
, ● the upper epidermis is transparent so light can pass through it to get to the palisade
layer
● the epidermal tissues are covered with a waxy cuticle so they can reduce the water lost
by transpiration
How are plants adapted to live in extreme environments?
● small leaves to reduce the surface area for water loss by evaporation
● hairs on the surface trap water vapour, reducing diffusion from the leaf to the air
● thick waxy cuticles to reduce water loss by evaporation
● fewer stomata/stomata that only open at night to reduce water loss by evaporation
● stomata in small pits which reduces air flow close to the stomata, reducing water loss
How can you estimate the rate of transpiration?
using a potometer. The air bubble moves along the tube as the plant loses water. The speed of
the bubble gives a measure of the rate of transpiration
explain the role of auxins in the growth responses of shoots to light
● shoots grow towards the light (positively phototropic)
● when the tip of the shoot is exposed to light, auxins move to the shaded side of the
shoot
● this makes the cells grow faster on the shaded side, so the shoot bends towards the light
explain the role of auxins in the growth responses of shoots to gravity
● shoots grow away from gravity (negatively gravitropic)
● when a shoot is growing sideways, auxins are pulled downwards by gravity, increasing
cell elongation so the shoot grows upwards
explain the role of auxins in growth responses of roots to light
● roots grow away from light (negatively phototropic)
● if a root is exposed to light, auxins move to the shaded side of the root
● the auxin inhibits cell elongation on the shaded side so the root bends downwards
explain the role of auxins in growth responses of roots to gravity
● roots grow towards gravity (positively gravitropic)
● when a root grows sideways, auxins are pulled downwards by gravity and inhibit cell
elongation so the root grows downwards
describe the commercial uses of auxins
● auxins are in selective weedkillers to kill plants that have broad leaves but not narrow
leaves
