B8- Photosynthesis ☀️🍀 Flashcards
What do plants use for their source of energy ?
- plants use [sun]light for their source of energy
What is photosynthesis?
- photosynthesis, is an endothermic reaction which plants use to trap light energy.
Where does photosynthesis take place ?
- photosynthesis takes place in the chloroplasts of a plant.
- this is because, the chloroplasts contain a chemical known as chlorophyll, which can trap light energy.
What are chloroplasts ?
Hint: organelles
- chloroplasts, are large organelles found inside plant cells
What is chlorophyll ?
- chlorophyll is a green pigment within chloroplasts, that trap light energy.
What is the difference between chlorophyll 🆚 chloroplasts ?
- chloroplasts, are large organelles found inside plant cells
- ; chlorophyll is a green pigment within chloroplasts, that trap light energy.
What is the word equation for photosynthesis ?
- carbon dioxide + water——> glucose + oxygen.
- [light is on the top of the arrow; chlorophyll is on the bottom of the arrow]
What are the stages of photosynthesis ?
Hint: the plant takes…
- the plant takes carbon dioxide and water into the leaf, then light energy is absorbed by chlorophyll.
- the light energy [absorbed/trapped by chlorophyll] is then used to convert the carbon dioxide and water, into the sugar glucose.
- and in this reaction, oxygen is also produced.
What is the chemical equation for photosynthesis ?
- 6CO2 + 6H20—-> C6 H12 O6 + 6O2
What can you tell me about a graph that measures the rate of photosynthesis, at each level of light intensity? [5]
- when the light intensity is zero, the rate of photosynthesis is zero. This is because plants need light to carry out photosynthesis.
- as we increase the light energy, the rate of photosynthesis decreases.
- since the plant now has more light energy to carry out photosynthesis, therefore the reaction gets faster.
- ; if we increase the light intensity, and the rate of photosynthesis also increases, this means the light intensity was limiting.
- and at this point, light intensity is a limiting factor.
if we increase the light intensity, and the rate of photosynthesis also increases, this means the light intensity was limiting. Why?
Hint: as fast
- photosynthesis wasn’t as fast as it could have been, as there wasn’t enough light.
What happens if we keep increasing the light intensity, after light intensity is a limiting factor ?
Hint: no longer, limiting factor
- if we keep increasing the light intensity, there comes a point where the rate of photosynthesis no longer increases.
- at this point, light intensity is no longer the limiting factor and something else is now of short supply- [e.g- level of carbon dioxide in the air]
What can you tell me about a graph that measures the rate of photosynthesis, at each level of carbon dioxide ?
Hints: zero
- when the level of carbon dioxide is zero, the rate of photosynthesis is zero. This is because plants need light to carry out photosynthesis.
- as we increase the carbon dioixide level, the rate of photosynthesis increases.
- ; if we increase the carbon dioxide level, and the rate of photosynthesis also increases, this means the light intensity was limiting.
- and at this point, carbon dioxide is the limiting factor.
What happens if we keep increasing the carbon dioxide level, after light intensity is a limiting factor ?
- if we keep increasing the carbon dioxide level, there comes a point where the rate of photosynthesis no longer increases.
- at this point, carbon dioxide level is no longer the limiting factor and something else is now of short supply.
Explain how the amount of chlorophyll [in a leaf], can be a limiting factor.
- For example, a leaf might have patches of chlorophyll.
- and since these leaves can trap less light energy than normal leaves, they’ll have a lower rate of photosynthesis.
What are the four limiting factors of photosynthesis ?
- the four limiting factors are:
- temperature
- light intensity
- level of carbon dioxide
- [amount of chlorophyll]
How can temperature be a limiting factor?
Hint: enzymes
- as we increase the temperature, the enzymes involved in photosynthesis work faster, meaning the rate of photosynthesis increases.
- ; if we keep increasing the temperature, the enzymes will denature and the rate of photosynthesis falls.
Describe how the leaf is adapted for photosynthesis
Hint: allow carbon dioxide
- leaves are adapted for photosynthesis since:
- they have: a large surface area, and contain openings, called stomata to allow carbon dioxide into the leaf and oxygen out.
Explain how adaptations of the leaf make photosynthesis efficient. [2]
Hint: epidermis, prevents water loss
- The internal structure of the leaf is also adapted to promote efficient photosynthesis since:
- the Epidermis is thin and transparent, allowing more light to reach the palisade cells.
- Thin cuticle made of wax [thin waxy cuticle], protects the leaf from infection and prevents water loss without blocking out light
Explain how adaptations of the leaf make photosynthesis efficient. [1]
Hint: cell layer
- the palisade cell layer at top of leaf is adapted to make photosynthesis efficient, to absorb more light and increase the rate of photosynthesis
Further explain how adaptations of the leaf, make photosynthesis efficient. [2]
Hint: spongy layer, palisade
- the spongy layer, has air spaces allowing gases to diffuse through the leaf
- the palisade cells contain many chloroplasts, to absorb all the available light
How do plants use glucose ? [2]
- to release energy in respiration [which takes places in the mitochondria]
- to produce the insoluble storage molecule starch, which can be converted back to glucose by the plant if needed.
What are some other ways that plants can use glucose ? [2]
Hint: cellulose, storage form
- in most plants, the glucose produced by photosynthesis, is converted to fats and oils, which are used by the plants as a storage form of energy.
- cellulose is also made from the glucose produced by photosynthesis, to strengthen the cell walls [of a plant]
How can plants use amino acids, from glucose ?
- to produce amino acids- amino acids are used by the plant to synthesise proteins.
- To make amino acids from glucose, as plants need to absorb nitrate ions from the soil.
Explain why plants convert glucose to starch for storage.
- Plants convert glucose to starch in photosynthesis for storage and long-term energy usage.
- ; since glucose is soluble it can affect how water moves in and out of the cell by osmosis [as it would affect the concentration gradient]
- so its converted to starch [which is soluble] so it’s more suitable for long-term storage.
How do plants convert glucose to starch, for storage ? [2]
- Glucose is converted into starch by the process called polymerization.
- In polymerization, several simple and soluble molecules of glucose are put together to form a complex, insoluble molecule of starch.
In simple terms, how can polymerisation be explained ? [2]
- Polymerisation is similar to constructing a large building out of the same type of small blocks.
- The blocks can be connected in various ways to create a larger, more intricately shaped structure.
Why is photosynthesis an endothermic reaction ?
- photosynthesis is an endothermic reaction because:
- photosynthesis takes in energy, which is transferred from the environment, to the chloroplasts by light.
