BIOLOGY PAPER 2 (KEY CONCEPTS ALSO CAN COME) There are 3 LIMITING FACTORS for photosynthesis. These stop
TOPIC 6 – PLANT STRUCTURES AND THEIR FUNCTIONS photosynthesis from happening any faster. Usually more than one
6.1 Describe photosynthetic organisms as the main producers is in effect at the same time.
of food and therefore biomass 1) LIGHT INTENSITY - Light is needed to transfer the
- PRODUCERS (eg. plants/algae) use energy from the sun to make energy needed for photosynth.
GLUCOSE. Some of this glucose is used to make larger molecules 1) As light intensity increases,
rate of photosynthesis also
that the plants can use to grow. This makes up the BIOMASS
increases as there is more light
(mass of a living thing). energy so the reaction happens
- The energy in the plant’s biomass moves up the food chain as faster
animals eat them and each other. 2) Eventually the graph will
- Thus photosynthetic organisms are the main producers of food plateau (flatten out) & raising
and thus biomass in all food webs and food chains. light intensity will have no effect
& is NOT the limiting factor. This
6.2 Describe photosynthesis in plants and algae as an
is because either temperature
endothermic reaction that uses light energy to react carbon or CO2 are the limiting factor.
dioxide and water to produce glucose and oxygen 2) CO2 CONCENTRATION - CO2 is one of the raw
- Photosynthesis happens inside CHLOROPLASTS which contain materials needed for
CHLOROPHYLL that absorb the light energy. The equation of photosynthesis
photosynthesis is: 1) As you increase CO2
concentration rate of
photosynthesis also increases.
2) The graph eventually flattens
out and is no longer the limiting
Carbon dioxide & water are taken in to produce glucose & oxygen factor
- This process can only happen in the presence of light as Energy is
transferred to the chloroplasts by lights 3) TEMPERATURE
- Photosynthesis is an ENDOTHERMIC process as light energy is 1) If the temperature is too low –
the enzymes needed for
taken in during the reaction
photosynthesis work more
6.3 Explain the effect of temperature, light intensity and slowly at low temperatures
carbon dioxide concentration as limiting factors on the rate of 2) If the temperature gets too
photosynthesis hot, the enzymes will denature
and so photosynthesis will not
happen
- Enzymes work fastest at the OPTIMUM TEMPERATURE
,6.4 Explain the interactions of temperature, light intensity and There are 2 ways of doing this practical:
carbon dioxide concentration in limiting the rate of a) Comparing colour change of sodium hydrogencarbonate
photosynthesis SETUP: 1) Place a lamp BEHIND beaker of water (this will act as a
- As shown above, usually it is not just one factor limiting the rate heat filter). Then place bottles at set distances from the lamp. Eg
of photosynthesis. When the graph flattens out it means 30, 40, 50 & 60cm from lamp and REMOVE bottle caps.
something is stopping photosynthesis from occurring. It could be 2) Add the SAME number of algae balls into each bottle (eg 15)
any of the three factors. 3) Add the same volume of sodium hydrogen carbonate indicator
6.5 Core Practical: Investigate the effect of light intensity on solution to each bottle. Put on bottle caps
the rate of photosynthesis 4) - Set up a CONTROL VARIABLE: Temperature is controlled by
- Photosynthesis is the process by which green plants and some beaker of water/LED bulb used (gives of low heat)
other organisms (eg pondweed/algae) use sunlight to synthesise - Set up NEGATIVE CONTROL: Cover one bottle in foil so it is in the
molecules of glucose & oxygen from carbon dioxide and water. dark and place next to the bottle closest to lamp. This should turn
- This practical investigates the effect of changing the light YELLOW as no photosynthesis happens so CO2 only increases
intensity on the rate of photosynthesis. (due to cellular respiration).
SODIUM HYDROGEN CARBONATE: This is an indicator showing PRACTICAL: 1) Switch on the lamp and set a timer for 60 minutes
the level of carbon dioxide: RESULTS: Compare the colours of the bottles.
COLOUR Concentration of CO2 - The bottles CLOSER to the lamp will be more PURPLE as rate of
YELLOW HIGHEST photosynthesis is HIGH so more CO2 is being taken in, so a less
ORANGE HIGH C02 concentration in the solution
RED ATMOSPHERIC LEVEL - The bottles FURTHER to the lamp will be more YELLOW as rate of
MAGENTA LOW photosynthesis is LOW so less CO2 is being taken in, so a higher
PURPLE LOWEST
C02 concentration in the solution#
- CO2 is USED UP during photosynthesis (it is one of the raw
a) Measuring the rate of oxygen production
materials) [CO2 + water -> glucose +oxygen]
Photosynthesis produces oxygen, so the more oxygen produced
- CO2 is PRODUCED in cellular respiration (glucose + O2 -> CO2)
the higher rate of photosynthesis. Algae or pondweed can be used
- Thus, if rate of photosynthesis is FASTER than rate of respiration
SETUP: There are 3 ways to setup this based on how you collect
then CO2 levels will DECREASE causing colour to be more
the oxygen:
PURPLE
1) In a flask of WATER, place the algae. Add sodium hydrogen
- If rate of photosynthesis is SLOWER than rate of respiration then
carbonate solution to make sure the plant has enough CO2 (it
CO2 levels will INCREASE causing colour to be more YELLOW
releases CO2 in a solution). Connect the flask to a gas syringe.
,2) In a test tube add the sodium hydrogencarbonate and water FORMULA to calculate light intensity:
with the algae balls. The number of oxygen bubbles released are
counted to see rate of oxygen.
- This method can introduce errors as all oxygen bubbles may not
contain the same amount of oxygen.
- This can be solved like a proportionality question
3) Place the pondweed into a funnel and INVERT it into a beaker
6.7 Explain how the structure of the root hair cells is adapted
full of water. Fill a test tube with water and then INVERT it onto the
to absorb water and mineral ions
FUNNEL. This way any oxygen produced will go up the funnel, into
- Roots are needed to absorb WATER & MINERAL IONS from the
the test tube, displacing the water so oxygen produced can be
soil.
measured.
- MINERAL IONS are absorbed by ACTIVE TRANSPORT. This is
PRACTICAL: 1) Place the set up apparatus at a set distance from
because there is usually a higher concentration of minerals in the
the lamp.
roots than in the soil.
2) In a set amount of time (eg 1 minute) measure/count how much
- WATER is absorbed by OSMOSIS
oxygen is produced.
To help increase this, root hair cells come out of the root to
3) Repeat experiment but place apparatus at different distances
increase surface area. It has the following adaptations:
from the lamp.
1) INCREASED SURFACE AREA: Each root is covered in many root
RESULTS: Across all methods you will see the further the
hair cells, so the surface area is increased as more soil comes in
pondweed/algae are from the lamp the LOWER rate of
contact with the roots, so more water/minerals can be absorbed
photosynthesis (as lower oxygen produced). This is due to a
2) HAS NO CHLOROPLASTS: As it is underground, they can’t
decrease in light intensity.
photosynthesise so don’t need chloroplasts
6.6 Explain how the rate of photosynthesis is directly
3) HAS LOTS OF MITOCHANDRIA: This releases energy needed for
proportional to light intensity and inversely proportional to the
active transport.
distance from a light source, including the use of the inverse
square law calculation
- The rate of photosynthesis is DIRECTLY PROPORTIONAL to the
light intensity. This is because the higher the light intensity, the
6.8 Explain how the structures of the xylem and phloem are
more energy to carry out photosynthesis
adapted to their function in the plant, including:
- Light Intensity is INDIRECTLY PROPORTIONAL to the distance.
a lignified dead cells in xylem transporting water and minerals
This is because as distance increases the light intensity decreases
through the plant
as the light is becomes more spread out. This means the rate of
b living cells in phloem using energy to transport sucrose
photosynthesis is also INDIRECTLY PROPORTIONAL to distance.
around the plant
, There are 2 types of transport vessels in plants: 6.9 Explain how water and mineral ions are transported
1) XYLEM: Used to transport WATER & MINERAL IONS from the through the plant by transpiration, including the structure and
roots to the stem to the leaves. function of the stomata
- The Xylem vessel walls are LIGNIFED. This means they are TRANSPIRATION: Water evaporation from the surface of leaves.
supported by LIGNIN. This is an impermeable substance that - Water is evaporated from leaves, so more water is passed from
strengthens the cell wall to stop them from bursting/contracting in the xylem into the leaf to replace the lost water. This causes more
low pressure water to be drawn from the roots – Thus there is a constant
- They are made of DEAD CELLS joined end to end with NO END TRANSPIRATION STREAM in the plant.
WALLS between them. Water can only move UPWARDS. - This is needed to provide water to the leaves for photosynthesis.
- They have NO CYTOPLASM and are just a HOLLOW TUBE to STOMATA: - Stomata are tiny pores on the bottom of the leaf that
allow water & mineral ions to pass through allow the diffusion of OXYGEN & CARBON DIOIXDE. It also allows
2) PHLOEM: In the leaves photosynthesis happens that creates WATER VAPOUR to escape through the leaf in transpiration.
glucose. This can be used to create other compounds and needs Stomata are surrounded by GUARD CELLS that change shape to
to be transported around the plant. control the size of the pore:
- The function of the phloem is to transport the food substances - In BRIGHTER conditions (day) the guard cells are TURGID
(mainly SUCROSE) made in the leaves to the rest of the plant for (swollen with water) causing the stomata to OPEN
either immediate use (to grow) or to be stored. - In DARKER conditions (night) the guard cells become FLACCID
- Molecules can be transported BOTH up & down the phloem (low on water & limp) causing the stomata to CLOSE
Phloem is made up of 2 types of tissue (both are LIVING): 6.10 Describe how sucrose is transported around the plant by
a) SIEVE TUBE ELEMENT CELL: A long line of cells arranged end to translocation
end, with small PORES in the end walls to allow phloem sap to - Translocation is when sucrose is transported along the PHLOEM
flow. Inside, almost all the organelles are lost and only some vessel around the plant. It can go up and down.
cytoplasm. This is to make room for the phloem sap. - Translocation requires ATP energy (from respiration).
- As phloem doesn’t have most organelles it can’t produce a lot of 6.12 Explain the effect of environmental factors on the rate of
ATP (energy produced by respiration) thus companion cells water uptake by a plant, to include light intensity, air
provide this energy. movement and temperature
b) COMPANION CELLS: Contain all the organelles and a lot of The RATE OF TRANSPIRATION is affected by 3 environmental
mitochondria. They are linked to the sieve tube element cells so it factors: 1) LIGHT INTENSITY: The brighter the light, the faster rate
can pass ATP to it. This supplies the energy needed for active of transpiration. This is because in light the stomata are open to
transport to move sucrose in/out of cells exchange gases, so water can be easily lost. In dark conditions,
the stomata are closed, so water can’t leave.
TOPIC 6 – PLANT STRUCTURES AND THEIR FUNCTIONS photosynthesis from happening any faster. Usually more than one
6.1 Describe photosynthetic organisms as the main producers is in effect at the same time.
of food and therefore biomass 1) LIGHT INTENSITY - Light is needed to transfer the
- PRODUCERS (eg. plants/algae) use energy from the sun to make energy needed for photosynth.
GLUCOSE. Some of this glucose is used to make larger molecules 1) As light intensity increases,
rate of photosynthesis also
that the plants can use to grow. This makes up the BIOMASS
increases as there is more light
(mass of a living thing). energy so the reaction happens
- The energy in the plant’s biomass moves up the food chain as faster
animals eat them and each other. 2) Eventually the graph will
- Thus photosynthetic organisms are the main producers of food plateau (flatten out) & raising
and thus biomass in all food webs and food chains. light intensity will have no effect
& is NOT the limiting factor. This
6.2 Describe photosynthesis in plants and algae as an
is because either temperature
endothermic reaction that uses light energy to react carbon or CO2 are the limiting factor.
dioxide and water to produce glucose and oxygen 2) CO2 CONCENTRATION - CO2 is one of the raw
- Photosynthesis happens inside CHLOROPLASTS which contain materials needed for
CHLOROPHYLL that absorb the light energy. The equation of photosynthesis
photosynthesis is: 1) As you increase CO2
concentration rate of
photosynthesis also increases.
2) The graph eventually flattens
out and is no longer the limiting
Carbon dioxide & water are taken in to produce glucose & oxygen factor
- This process can only happen in the presence of light as Energy is
transferred to the chloroplasts by lights 3) TEMPERATURE
- Photosynthesis is an ENDOTHERMIC process as light energy is 1) If the temperature is too low –
the enzymes needed for
taken in during the reaction
photosynthesis work more
6.3 Explain the effect of temperature, light intensity and slowly at low temperatures
carbon dioxide concentration as limiting factors on the rate of 2) If the temperature gets too
photosynthesis hot, the enzymes will denature
and so photosynthesis will not
happen
- Enzymes work fastest at the OPTIMUM TEMPERATURE
,6.4 Explain the interactions of temperature, light intensity and There are 2 ways of doing this practical:
carbon dioxide concentration in limiting the rate of a) Comparing colour change of sodium hydrogencarbonate
photosynthesis SETUP: 1) Place a lamp BEHIND beaker of water (this will act as a
- As shown above, usually it is not just one factor limiting the rate heat filter). Then place bottles at set distances from the lamp. Eg
of photosynthesis. When the graph flattens out it means 30, 40, 50 & 60cm from lamp and REMOVE bottle caps.
something is stopping photosynthesis from occurring. It could be 2) Add the SAME number of algae balls into each bottle (eg 15)
any of the three factors. 3) Add the same volume of sodium hydrogen carbonate indicator
6.5 Core Practical: Investigate the effect of light intensity on solution to each bottle. Put on bottle caps
the rate of photosynthesis 4) - Set up a CONTROL VARIABLE: Temperature is controlled by
- Photosynthesis is the process by which green plants and some beaker of water/LED bulb used (gives of low heat)
other organisms (eg pondweed/algae) use sunlight to synthesise - Set up NEGATIVE CONTROL: Cover one bottle in foil so it is in the
molecules of glucose & oxygen from carbon dioxide and water. dark and place next to the bottle closest to lamp. This should turn
- This practical investigates the effect of changing the light YELLOW as no photosynthesis happens so CO2 only increases
intensity on the rate of photosynthesis. (due to cellular respiration).
SODIUM HYDROGEN CARBONATE: This is an indicator showing PRACTICAL: 1) Switch on the lamp and set a timer for 60 minutes
the level of carbon dioxide: RESULTS: Compare the colours of the bottles.
COLOUR Concentration of CO2 - The bottles CLOSER to the lamp will be more PURPLE as rate of
YELLOW HIGHEST photosynthesis is HIGH so more CO2 is being taken in, so a less
ORANGE HIGH C02 concentration in the solution
RED ATMOSPHERIC LEVEL - The bottles FURTHER to the lamp will be more YELLOW as rate of
MAGENTA LOW photosynthesis is LOW so less CO2 is being taken in, so a higher
PURPLE LOWEST
C02 concentration in the solution#
- CO2 is USED UP during photosynthesis (it is one of the raw
a) Measuring the rate of oxygen production
materials) [CO2 + water -> glucose +oxygen]
Photosynthesis produces oxygen, so the more oxygen produced
- CO2 is PRODUCED in cellular respiration (glucose + O2 -> CO2)
the higher rate of photosynthesis. Algae or pondweed can be used
- Thus, if rate of photosynthesis is FASTER than rate of respiration
SETUP: There are 3 ways to setup this based on how you collect
then CO2 levels will DECREASE causing colour to be more
the oxygen:
PURPLE
1) In a flask of WATER, place the algae. Add sodium hydrogen
- If rate of photosynthesis is SLOWER than rate of respiration then
carbonate solution to make sure the plant has enough CO2 (it
CO2 levels will INCREASE causing colour to be more YELLOW
releases CO2 in a solution). Connect the flask to a gas syringe.
,2) In a test tube add the sodium hydrogencarbonate and water FORMULA to calculate light intensity:
with the algae balls. The number of oxygen bubbles released are
counted to see rate of oxygen.
- This method can introduce errors as all oxygen bubbles may not
contain the same amount of oxygen.
- This can be solved like a proportionality question
3) Place the pondweed into a funnel and INVERT it into a beaker
6.7 Explain how the structure of the root hair cells is adapted
full of water. Fill a test tube with water and then INVERT it onto the
to absorb water and mineral ions
FUNNEL. This way any oxygen produced will go up the funnel, into
- Roots are needed to absorb WATER & MINERAL IONS from the
the test tube, displacing the water so oxygen produced can be
soil.
measured.
- MINERAL IONS are absorbed by ACTIVE TRANSPORT. This is
PRACTICAL: 1) Place the set up apparatus at a set distance from
because there is usually a higher concentration of minerals in the
the lamp.
roots than in the soil.
2) In a set amount of time (eg 1 minute) measure/count how much
- WATER is absorbed by OSMOSIS
oxygen is produced.
To help increase this, root hair cells come out of the root to
3) Repeat experiment but place apparatus at different distances
increase surface area. It has the following adaptations:
from the lamp.
1) INCREASED SURFACE AREA: Each root is covered in many root
RESULTS: Across all methods you will see the further the
hair cells, so the surface area is increased as more soil comes in
pondweed/algae are from the lamp the LOWER rate of
contact with the roots, so more water/minerals can be absorbed
photosynthesis (as lower oxygen produced). This is due to a
2) HAS NO CHLOROPLASTS: As it is underground, they can’t
decrease in light intensity.
photosynthesise so don’t need chloroplasts
6.6 Explain how the rate of photosynthesis is directly
3) HAS LOTS OF MITOCHANDRIA: This releases energy needed for
proportional to light intensity and inversely proportional to the
active transport.
distance from a light source, including the use of the inverse
square law calculation
- The rate of photosynthesis is DIRECTLY PROPORTIONAL to the
light intensity. This is because the higher the light intensity, the
6.8 Explain how the structures of the xylem and phloem are
more energy to carry out photosynthesis
adapted to their function in the plant, including:
- Light Intensity is INDIRECTLY PROPORTIONAL to the distance.
a lignified dead cells in xylem transporting water and minerals
This is because as distance increases the light intensity decreases
through the plant
as the light is becomes more spread out. This means the rate of
b living cells in phloem using energy to transport sucrose
photosynthesis is also INDIRECTLY PROPORTIONAL to distance.
around the plant
, There are 2 types of transport vessels in plants: 6.9 Explain how water and mineral ions are transported
1) XYLEM: Used to transport WATER & MINERAL IONS from the through the plant by transpiration, including the structure and
roots to the stem to the leaves. function of the stomata
- The Xylem vessel walls are LIGNIFED. This means they are TRANSPIRATION: Water evaporation from the surface of leaves.
supported by LIGNIN. This is an impermeable substance that - Water is evaporated from leaves, so more water is passed from
strengthens the cell wall to stop them from bursting/contracting in the xylem into the leaf to replace the lost water. This causes more
low pressure water to be drawn from the roots – Thus there is a constant
- They are made of DEAD CELLS joined end to end with NO END TRANSPIRATION STREAM in the plant.
WALLS between them. Water can only move UPWARDS. - This is needed to provide water to the leaves for photosynthesis.
- They have NO CYTOPLASM and are just a HOLLOW TUBE to STOMATA: - Stomata are tiny pores on the bottom of the leaf that
allow water & mineral ions to pass through allow the diffusion of OXYGEN & CARBON DIOIXDE. It also allows
2) PHLOEM: In the leaves photosynthesis happens that creates WATER VAPOUR to escape through the leaf in transpiration.
glucose. This can be used to create other compounds and needs Stomata are surrounded by GUARD CELLS that change shape to
to be transported around the plant. control the size of the pore:
- The function of the phloem is to transport the food substances - In BRIGHTER conditions (day) the guard cells are TURGID
(mainly SUCROSE) made in the leaves to the rest of the plant for (swollen with water) causing the stomata to OPEN
either immediate use (to grow) or to be stored. - In DARKER conditions (night) the guard cells become FLACCID
- Molecules can be transported BOTH up & down the phloem (low on water & limp) causing the stomata to CLOSE
Phloem is made up of 2 types of tissue (both are LIVING): 6.10 Describe how sucrose is transported around the plant by
a) SIEVE TUBE ELEMENT CELL: A long line of cells arranged end to translocation
end, with small PORES in the end walls to allow phloem sap to - Translocation is when sucrose is transported along the PHLOEM
flow. Inside, almost all the organelles are lost and only some vessel around the plant. It can go up and down.
cytoplasm. This is to make room for the phloem sap. - Translocation requires ATP energy (from respiration).
- As phloem doesn’t have most organelles it can’t produce a lot of 6.12 Explain the effect of environmental factors on the rate of
ATP (energy produced by respiration) thus companion cells water uptake by a plant, to include light intensity, air
provide this energy. movement and temperature
b) COMPANION CELLS: Contain all the organelles and a lot of The RATE OF TRANSPIRATION is affected by 3 environmental
mitochondria. They are linked to the sieve tube element cells so it factors: 1) LIGHT INTENSITY: The brighter the light, the faster rate
can pass ATP to it. This supplies the energy needed for active of transpiration. This is because in light the stomata are open to
transport to move sucrose in/out of cells exchange gases, so water can be easily lost. In dark conditions,
the stomata are closed, so water can’t leave.
