Extra questions B8 Flashcards
Explain why a leaf kept in the light for 24 hours will turn an iodine solution blue/black, whereas a leaf kept in light for 24 hours and then dark for 24 hours will have no effect on the iodine solution
- Leaf kept in light photosynthesises, making glucose from carbon dioxide and water using energy from light.
- Glucose converted to starch to be stored and used for respiration when leaf is in dark and cannot photosynthesise.
- Iodine solution turns blue‑black in presence of starch, because plant has been photosynthesising for a long time and glucose will have been stored as starch.
- If leaf is then kept in dark for 24 hours it cannot photosynthesise so cells will use stored starch for respiration. Little or no starch left in the leaves so iodine solution unaffected.
Describe the path taken by a carbon atom as it moves from being part of the carbon dioxide in the air to being part of a starch molecule in a plant
Carbon atom moves from air into air spaces in leaf, into plant cells, into chloroplasts, joins with water to make glucose, and is converted to starch for storage.
Explain in terms of limiting factors why the plants growing in a tropical rainforest are so much bigger than the plants that grow in a UK woodland, and why both are bigger than the plants on the Arctic tundra
- Tropical rainforest: high light intensity, warm temperature, plenty of moisture, carbon dioxide from decaying material
- relatively few limiting factors and rapid growth conditions available all year round, allowing plants and even individual leaves get very large);
- UK woodland: low light intensity, short days in winter, cold temperature
- (most growth takes place in spring and summer with plenty of light and warmth but temperatures still lower temperatures than tropical rain forest, less time for growth so plants smaller);
- Arctic tundra: no light all winter but lots of light in summer, lack of water due to frozen ground
- (low temperatures limiting factor on photosynthesis for most of year, so plants much smaller and slower-
growing than tropical rainforest or UK woodland)
Explain why pitcher plants, sundews and Venus fly traps are often found growing in bogs globally, an environment where not many other plants can survive
- Bogs are wet and peaty and soil contains very few minerals, especially nitrates.
- Plants need nitrates from soil to make amino acids and build them into proteins.
- Many plants cannot grow well in bogs. Carnivorous plants trap insects and digest their bodies, which provide good supply of nitrates and other minerals.
- These plants can grow and thrive in bogs as they do not rely on bog soil for minerals.
Why is light needed for photosynthesis?
to transfer energy
Plants need energy to make glucose.
How do plants get this energy?
light is trapped/ absorbed by chloroplasts
Explain the results when the light intensity was 0 lux.
when there is no light there is no photosynthesis
no oxygen is produced
respiration happens and oxygen is used
overall oxygen production is negative
Explain the overall exchange of carbon dioxide and oxygen at the three different light intensities.
Bright light:
* rate of photosynthesis is high due to high light intensity
* carbon dioxide is absorbed from the air
*oxygen is released into the air
Dim light:
* no exchange of carbon dioxide or oxygen with the air
* rate of respiration equals rate of photosynthesis
No Light:
* no photosynthesis occurs as no light
* no carbon dioxide is absorbed and no oxygen released
* plant respires so takes in oxygen and releases carbon dioxide into the air
Suggest why the funnel is supported on pieces of plasticine
To allow water to circulate and provide carbon dioxide to pondweed
A leaf is tested for starch. The green part of the leaf is stained black. The white part of the leaf is stained orange. What conclusion can you make from this result
Chlorophyll is needed to make starch
Describe how plants make starch from simple raw materials
- carbon dioxide is needed and absorbed from the air
- Water is needed and absorbed from the soil
- Light is required and it is absorbed by chlorophyll
- This allows photosynthesis to occur to pride glucose
- The glucose join together to make starch
Describe how the palisade mesophyll layer is adapted for photosynthesis
- lots of chlorophyll
- packed closely together to maximise surface area exposed to light
What is the function of stomata
the cells open and close the stomata to control water loss and gas exchange from the leaves
Describe how a student would find out if the liquid from the leaf contained glucose
- add Benedict’s solution to the liquid
- boil the solution
- if glucose is resent the colour will change from blue to brick red
Describe how the students could find out if the liquid from the leaf contained starch
- add iodine solution to the liquid
- if starch is present it changes colour from orange/brown to blue/black
Explain why the leaf in light for four days contained both glucose and starch
- Glucose is made from photosynthesis
- excess glucose is converted into starch
Explain why the leaf left in a cupboard with no light for two days contained glucose but not starch
- starch stores have been converted into glucose
- so the glucose can be used for respiration
- because there is no light to make more glucose by photosynthesis
The teacher suggests putting the boiling tube in a beaker of water during the investigation. Suggest why this would make the results more valid.
Prevents temperature affecting photosynthesis
State one error the student has made in completing the results at 20 cm
The number is not rounded
What evidence in table 1 shows that the data is repeatable
The number of bubbles at each distance are similar to
Energy is released during respiration. Give two uses of the energy released.
- Active transport
- Making cellulose
Explain why the concentration of carbon dioxide in the tube stayed the same between day 0 and day 5
- the pondweed was taking in regular amounts of carbon dioxide to photosynthesise
- the snail and pondweed were both respiring to produce CO2
On day 10, the pond snail died. Explains why the concentration of carbon dioxide increased after day 10
- the snail is being broken down
- by bacteria in the pond water
- therefore the respiration of bacteria increases the CO2
Describe how energy for photosynthesis is gained by plants
Light is captured by chlorophyll
