Photosynthesis Flashcards
What is the equation for photosynthesis?
Water + carbon dioxide -> glucose + oxygen
6H2O + 6CO2 -> C6H12O6 + 6O2
- Light energy is absorbed by a green substance called chlorophyll.
- This energy is used to convert carbon dioxide and water into sugar (glucose).
- Oxygen is released as a by-product.
How is a leaf adapted for photosynthesis?
It needs carbon dioxide, light and water so:
- Large surface area of leaves to absorb light - wide and flat leaves with waxy cuticle to prevent water loss
- Thin surface to allow gases in with short diffusion distance - spongy mesophyll not tightly packed allowing CO2 in with irregular cells
- Leaves contain chlorophyll in chloroplasts to absorb light - palisade cells, block shaped and packed into layers
- Veins a)carry water through xylem to leaf cells and b)glucose away through phloem and c)to support leaves
- Stomata are pores on underside of leaves which allow gases to move in and out
- Guard cells that open and close the stomata to regulate gas exchange and on bottom of leaf to limit water loss
What factors affect rate of photosynthesis and why?
These are “limiting factors”
- Amount of light
- Amount of carbon dioxide
- Temperature
- Chlorophyll levels in the leaf
Why is photosynthesis an endothermic reaction?
- It is endothermic because it takes energy from its surroundings eg heat, light, carbon dioxide and water.
- The energy transferred from the environment when bonds holding carbon dioxide and water are broken is more than that transferred back to the environment with the formation of new bonds in glucose and oxygen
- The extra energy is transferred by light
What does photosynthesis do?
- Plants don’t eat but make their own food by photosynthesis
- Photosynthesis takes place in green part of plants esp. leaves
- Photosynthesis takes place in the light
Explain the process of photosynthesis?
- Plant leaves/algae cells are full of chloroplasts
- Chloroplasts contain chlorophyll
- Energy transferred from environment to chloroplasts by light.
- Energy is transferred to convert carbon dioxide from the air and water from soil.
- This produces simple sugar called glucose with oxygen as by product
- Oxygen released into air
How is the glucose used by the plant?
- Some is used immediately by cells for respiration.
- Most is converted into insoluble starch and stored.
- Some is used to build up glucose into cellulose and complex carbohydrates
- To make amino acids combining sugars with nitrate ions and mineral ions in the soil
- To make fat or oil for storage
- To make proteins - plants also use nitrate ions from soil
How do algae photosynthesise?
- Algae are aquatic so photosynthesise in water.
- Large surface area absorbing carbon dioxide from surrounding water.
- Oxygen produced dissolves into water when released
How can plants help the environment
Plants absorb carbon dioxide so
- more photosynthesis will remove more carbon dioxide and help reduce global warming
- More photosynthesis will also produce more crops for food.
How does light affect photosynthesis?
Light intensity is the most obvious factor affecting rate of photosynthesis
If there is little or no light then photosynthesis will stop
The brighter the light the faster the rate of photosynthesis
How does temperature affect photosynthesis
Temperature affects all chemical reactions including photosynthesis.
Rate of photosynthesis with temperature rise as the reaction rate speeds up.
Photosynthesis controlled by enzymes
Most enzymes denature when temperature rises to over 40C
When enzymes denature rate of photosynthesis falls
How does carbon dioxide concentration affect photosynthesis
The atmosphere has 0.04% carbon dioxide
This limits rate of photosynthesis
On a sunny day carbon dioxide concentration is the most limiting factor
Increasing carbon dioxide concentration increases rate of photosynthesis
Carbon dioxide levels rise at night because plants respire but don’t photosynthesise in the dark.
So in the morning as light and temperature rise most carbon dioxide around plant gets used up.
In a lab or greenhouse carbon dioxide levels can be increased to speed up photosynthesis but outside light,heat and carbon dioxide are all limiting factors
How do chlorophyll levels in the leaf affect photosynthesis
If chlorophyll levels in a leaf are limited less photosynthesis will occur
If the plant has insufficient minerals especially magnesium it cannot make chlorophyll and plant may die.
Variegated leaves grow less vigorously because less chlorophyll
How do plants and algae use glucose
- Some glucose is used in respiration, providing energy for cells as it is broken down. Respiration is the reverse of photosynthesis
- Plants build up glucose into complex carbohydrates eg cellulose to strengthen cell walls
- Produce starch for storage. Starch is insoluble but glucose is soluble.
- To make amino acids by combining sugars with nitrate ions and other minerals ions like proteins
- To make fats and oils-lipids
- Mixes with magnesium to make chlorophyll
Why do plants use cellulose
Glucose builds up smaller molecules into bigger ones
Makes complex carbohydrates like cellulose to strengthen cell walls
Why do plants make and store starch
Glucose converts to starch
- Glucose is soluble so could affect how water moves by osmosis and affect water balance of whole plant
- Starch is insoluble in water so has no effect on water balance and plants can store lots of it - no osmotic effect
- Main energy store for when dark or light levels low- found in cells all over the plant
- Also in special storage areas eg bulbs, tubors to help survive winter
- Starch has a compact shape
- Humans use these eg potato and onions
How do amino acids help plants
- Glucose combines with nitrate and other ions
- Build up into proteins eg enzymes
- Algae make amino acids using ions from surrounding water
- Low mineral areas eg bogs make growth difficult
- Some plants survive low mineral soil by taking nutrients from insects eg Venus fly trap using enzymes to digest insects
Why do plants need lipids
- Lipids may be used as an energy store
- To make cell walls stronger
- Energy store in seeds providing food for new plant as it germinates
- Some algae possible biofuels
How does a greenhouses affect rate of photosynthesis?
Glass or plastic helps control environment
Atmosphere is warmer inside than outside and speeds up photosynthesis
Crops grow better and flower quicker
Can be used to grow fruit that doesn’t grow well outside eg peaches
How can you control limiting factors
Greenhouses control amount of light, temperature and carbon dioxide to find fastest rate of photosynthesis.
Can also be grown in water with perfect mineral balance - hydroponics.
The crops are soil free and there is no need to plough
The cost and economics are very important
Which part of the leaf is involved in photosynthesis
Palisade cells
How do we test for starch in plants eg potatoes
Iodine solution turns blue/black in presence of starch
The plant leaves need to be boiled to remove waxy coating and left in iodine
Describe ways to decrease rate of photosynthesis
It is an endothermic reaction needing light energy. It needs carbon dioxide It needs a warm temperature It also needs water It also needs nutrients
In which part of the plant does photosynthesis take place
Chloroplasts
