B8- Photosynthesis ☀️🍀

Question 1

What do plants use for their source of energy ?

Answer 1

• plants use [sun]light for their source of energy

Question 2

What is photosynthesis?

Answer 2

• photosynthesis, is an endothermic reaction which plants use to trap light energy.

Question 3

Where does photosynthesis take place ?

Answer 3

• 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.

Question 4

What are chloroplasts ?

Hint: organelles

Answer 4

• chloroplasts, are large organelles found inside plant cells

Question 5

What is chlorophyll ?

Answer 5

• chlorophyll is a green pigment within chloroplasts, that trap light energy.

Question 6

What is the difference between chlorophyll 🆚 chloroplasts ?

Answer 6

• chloroplasts, are large organelles found inside plant cells
• ; chlorophyll is a green pigment within chloroplasts, that trap light energy.

Question 7

What is the word equation for photosynthesis ?

Answer 7

• carbon dioxide + water——> glucose + oxygen.
• [light is on the top of the arrow; chlorophyll is on the bottom of the arrow]

Question 8

What are the stages of photosynthesis ?

Hint: the plant takes…

Answer 8

• 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.

Question 9

What is the chemical equation for photosynthesis ?

Answer 9

• 6CO2 + 6H20—-> C6 H12 O6 + 6O2

Question 10

What can you tell me about a graph that measures the rate of photosynthesis, at each level of light intensity? [5]

Answer 10

• 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.

Question 11

if we increase the light intensity, and the rate of photosynthesis also increases, this means the light intensity was limiting. Why?

Hint: as fast

Answer 11

• photosynthesis wasn’t as fast as it could have been, as there wasn’t enough light.

Question 12

What happens if we keep increasing the light intensity, after light intensity is a limiting factor ?

Hint: no longer, limiting factor

Answer 12

• 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]

Question 13

What can you tell me about a graph that measures the rate of photosynthesis, at each level of carbon dioxide ?

Hints: zero

Answer 13

• 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.

Question 14

What happens if we keep increasing the carbon dioxide level, after light intensity is a limiting factor ?

Answer 14

• 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.

Question 15

Explain how the amount of chlorophyll [in a leaf], can be a limiting factor.

Answer 15

• 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.

Question 16

What are the four limiting factors of photosynthesis ?

Answer 16

• the four limiting factors are:
• temperature
• light intensity
• level of carbon dioxide
• [amount of chlorophyll]

Question 17

How can temperature be a limiting factor?

Hint: enzymes

Answer 17

• 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.

Question 18

Describe how the leaf is adapted for photosynthesis

Hint: allow carbon dioxide

Answer 18

• 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.

Question 19

Explain how adaptations of the leaf make photosynthesis efficient. [2]

Hint: epidermis, prevents water loss

Answer 19

• 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

Question 21

Explain how adaptations of the leaf make photosynthesis efficient. [1]

Hint: cell layer

Answer 21

• the palisade cell layer at top of leaf is adapted to make photosynthesis efficient, to absorb more light and increase the rate of photosynthesis

Question 21

Further explain how adaptations of the leaf, make photosynthesis efficient. [2]

Hint: spongy layer, palisade

Answer 21

• 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

Question 22

How do plants use glucose ? [2]

Answer 22

• 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.

Question 23

What are some other ways that plants can use glucose ? [2]

Hint: cellulose, storage form

Answer 23

• 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]

Question 24

How can plants use amino acids, from glucose ?

Answer 24

• 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.

Question 25

Explain why plants convert glucose to starch for storage.

Answer 25

• 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.

Question 26

How do plants convert glucose to starch, for storage ? [2]

Answer 26

• 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.

Question 27

In simple terms, how can polymerisation be explained ? [2]

Answer 27

• 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.

Question 28

Why is photosynthesis an endothermic reaction ?

Answer 28

• photosynthesis is an endothermic reaction because:
• photosynthesis takes in energy, which is transferred from the environment, to the chloroplasts by light.