B8 - Photosynthesis

Question 1

What is an endothermic reaction?

Answer 1

a reaction that requires a transfer of energy from the environment

Question 2

What is glucose?

Answer 2

a simple sugar

Question 3

What are limiting factors?

Answer 3

factors that limit the rate of a reaction

Question 4

What is photosynthesis?

Answer 4

the process by which plants make food using carbon dioxide, water, and light

Question 5

What is the word equation for Photosynthesis?

Answer 5

Carbon Dioxide + water —(light)—> glucose + oxygen

Question 6

What is the balanced symbol equation for photosynthesis?

Answer 6

6H₂O + 6CO₂ —(light)—> C₆H₁₂O₆ + 6O₂

Question 7

What part of the leaf absorbs the energy from the sun?

Answer 7

The chlorophyll in the chloroplasts

Question 8

What type of reaction is photosynthesis and why?

Answer 8

Photosynthesis is an endothermic reaction, this is because energy is transferred from the environment when the light is absorbed by the chlorophyll

Question 9

What is the formula of glucose?

Answer 9

C₆H₁₂O₆

Question 10

What happens to the glucose produced during photosynthesis?

Answer 10

Some of the glucose is immediately used by the plant cells for respiration, however much of it is converted into insoluble starch and is stored.

Question 11

Explain the process of photosynthesis

Answer 11

Photosynthesis is an endothermic reaction used by plants to make their own food. Energy is required in the form of light from the sun. Light energy is absorbed by the chlorophyll in the chloroplasts in the leaf. This energy is then used to convert Carbon Dioxide (absorbed from the air through the stomata) and water (absorbed from the ground through the roots) into glucose. This chemical reaction also produces oxygen as a by-product. The oxygen is released into the air

Question 12

What leaf adaptations are there to make photosynthesis more efficient?

Answer 12

• Most leaves are broad
• Most leaves are thin
• They contain chlorophyll within chloroplasts
• They contain veins
• They contain air spaces
• They have guard cells

Question 13

How does having broad leaves make photosynthesis more efficient?

Answer 13

Broader leaves means that there is more surface area for the light to fall on

Question 14

How does having thin leaves make photosynthesis more efficient?

Answer 14

Thinner leaves means that the diffusion distances for the gases are short

Question 15

How does containing chlorophyll in chloroplasts make photosynthesis more efficient?

Answer 15

Chlorophyll within the chloroplasts absorbs the light which is needed to provide energy for photosynthesis

Question 16

How does having veins make photosynthesis more efficient?

Answer 16

Leaf veins contain xylem and phloem in vascular bundles. The xylem brings in plenty of water to the cells of the leaves and the phloem removes the products of photosynthesis (Glucose)

Question 17

How does having air spaces make photosynthesis more efficient?

Answer 17

Having air spaces in a leaf means that carbon dioxide can diffuse into the cells, and oxygen can diffuse out of the cells

Question 18

How does having guard cells make photosynthesis more efficient?

Answer 18

Guard cells open and close the stomata to regulate gas exchange

Question 19

How is algae adapted for photosynthesis

Answer 19

Algae is aquatic so they have a large surface area and can absorb carbon dioxide dissolved in the water around them, they also release the oxygen that they produce which dissolves into the water

Question 20

State 4 limiting factors of photosynthesis:

Answer 20

• Light
• Temperature
• Carbon Dioxide Concentration
• Chlorophyll levels in the leaf

Question 21

Explain how light is a limiting factor

Answer 21

If there is plenty of light then lots of photosynthesis can take place, if there a lack of light, photosynthesis would slow down. If there is no light, photosynthesis would stop. This is because light transfers the energy needed for the process. Even on sunny days, light may be limited due to shade from other plants or buildings. For most plants, the brighter and more intense the light is, the faster the rate of photosynthesis

Question 22

Explain how temperature is a limiting factor

Answer 22

Temperature affects all chemical reactions, including photosynthesis. Photosynthesis is controlled by enzymes, if it is too cold the reactant particles will not have much kinetic energy, reducing the number of collisions, the enzymes will also not work as effectively. As temperature increases, the rate of photosynthesis speeds up as the particles gain more kinetic energy and there is more collision between reactants and enzymes. However, if the temperature continues to rise, the enzymes will become denatured at around 40-50*C, this will cause the rate of photosynthesis to fall eventually to 0.

Question 23

Explain how Carbon Dioxide concentration is a limiting factor

Answer 23

Plants need Carbon Dioxide to perform photosynthesis. However, the atmosphere is only about 0.04% carbon dioxide. This means that carbon dioxide often limits the rate of photosynthesis. Increasing the carbon dioxide concentration will increase the rate of photosynthesis

Question 24

Explain how Chlorophyll levels in the leaf is a limiting factor

Answer 24

If the amount of chlorophyll in a leaf is limited in any way, less photosynthesis will take place. The leaves on some ornamental plants have white, chlorophyll-free areas. This reduces the rate of photosynthesis, causing the plants to grow less vigorously than plants with all green leaves. This is because chlorophyll in chloroplasts absorb the light that transfers the energy needed for the process.

Question 25

Describe the method for how the rate of photosynthesis is effected by light intensity:

Answer 25

1) Cut a piece of pondweed 8-10cm long. Place it in a boiling tube of water with the cut end uppermost
2) Use the thermometer to measure the temperature of the water in the boiling tube
3) Place the boiling tube in the large beaker of water, making sure that the top of the boiling tube is floating above the surface of the water in the beaker
Place the lamp 15cm from the boiling tube. Place the large beaker of water between the lamp and the boiling tube
4) Wait until there is a steady flow of bubbles from the cut end of the pondweed. Count the number of bubbles in 2 minutes. Record this in your results table.
5) Measure the temperature of the water in the boiling tube to make sure it has not changed.
6) Repeat steps 1-5 four more times but in step 3 increase the distance between the lamp and boiling tube by 2cm each time
7) Repeat the whole investigation (steps 1-6) two more times and record your results
8) Calculate the mean number of bubbles for each distance, leaving out any anomalous results.
9) Record data in appropriate table/graph

Question 26

What is the equation for light intensity?

Answer 26

Light intensity = 1 / (distance²)

Question 27

How do plants use glucose produced during photosynthesis?

Answer 27

• For respiration
• To convert into insoluble starch
• To produce fats and oils
• To produce cellulose
• To produce amino acids

Question 28

Why do plants use glucose produced in photosynthesis for respiration?

Answer 28

Plant and algal cells, like all other living cells, need to respire all the time. They use some of the glucose produced during photosynthesis as they respire. The glucose is broken down using oxygen to provide energy for the cells. Carbon dioxide and water are waste products of the reaction. Chemically, respiration is the reverse of photosynthesis

Question 29

Why do plants convert glucose produced in photosynthesis into insoluble starch?

Answer 29

Plants convert some glucose produced in photosynthesis into starch to be stored. Glucose is soluble in water. If it were stored in plant cells, it could affect the way water moved in and out of the cells by osmosis. Lots of glucose could affect the water balance of the whole plant. Starch is insoluble in water, this means that it has no effect on the water balance of the plant so plants can store large amounts of starch in their cells. Starch is the main energy store in plants and it is found in cells all over a plant:

• Starch is often stored in the cells of the leaves. It provides an energy store for when it is dark or when light levels are low
• Starch is also kept in special storage areas of a plant. For example, many plants produce tubers and bulbs that are full of stored starch to help them survive through the winter

Question 30

Why do plants use glucose produced in photosynthesis to produce lipids?

Answer 30

Plants and algae use some of the glucose from photosynthesis and energy transferred from respiration to build up fats and oils. These may be used in the cells as an energy store. They are sometimes used in the cell walls to make them stronger. In addition, plants often use fats or oils as an energy store in their seeds. Seeds provide food for the new plant to respire as it germinates.

Question 31

Why do plants use glucose produced in photosynthesis to produce cellulose?

Answer 31

Energy transferred in respiration may be used to build smaller molecules into bigger molecules. For example, plants build up glucose into complex carbohydrates such as cellulose. They use this to strengthen their cell wall.

Question 32

Why do plants use glucose produced in photosynthesis to produce amino acids?

Answer 32

Plants use some of the glucose from photosynthesis to make amino acids. They do this by combining sugars with nitrate ions and other mineral ions from the soil. These amino acids are then used for protein synthesis to make proteins. These proteins can then be used in the plant in many ways, including making enzymes. This uses energy from respiration. For this, the plant must be able to absorb nitrates and other minerals from the soil

Question 33

Can plants photosynthesise at night and why?

Answer 33

Plants cannot photosynthesise at night as there is no light, this means that photosynthesises stops

Question 34

Can plants respire at night and why?

Answer 34

Plants can respire 24 hours a day as they do not need light to respire, unlike photosynthesis

Question 35

What is the rate of photosynthesis compared to the rate of respiration of a plant in a completely dark room?

Answer 35

Photosynthesis stops but respiration continues

Question 36

What is the rate of photosynthesis compared to the rate of respiration of a plant in a dim light?

Answer 36

Photosynthesis rate = respiration rate

Question 37

What is the rate of photosynthesis compared to the rate of respiration of a plant in a bright light?

Answer 37

Photosynthesis rate > respiration rate

Question 38

What happens to the gas exchange in a plant at night and why?

Answer 38

Oxygen is taken in and Carbon Dioxide is given out, this is because respiration continues but photosynthesis stops

Question 39

What happens to the gas exchange in a plant under a dim light and why?

Answer 39

The net amount of oxygen in and out and Carbon dioxide in and out is 0, this is because the rate of photosynthesis is equal to the rate of respiration

Question 40

What happens to the gas exchange in a plant under a bright light and why?

Answer 40

More Carbon dioxide is taken in and more oxygen is given out, this is because the rate of photosynthesis is more than the rate of respiration.

Question 41

How are some carnivorous plants adapted to live in nitrate-poor soil such as bogs?

Answer 41

Some carnivorous plants, such as pitcher plants or Venus fly traps, are adapted to live in nitrate-poor soil. They can survive because they obtain most their nutrients from the animals, such as insects, that they catch. The plants produce enzymes to digest the insects they trap. They then use nitrates and other minerals from the digested bodies of their victims in place of nutrients they cannot get from the poor soil that they grow in

Question 42

What happens if a plant begins to photosynthesise faster?

Answer 42

It grows faster and creates more biomass

Question 43

How do farmers increase the yield of their crop?

Answer 43

They can use greenhouses or huge plastic polytunnels to try and remove limiting factors

Question 44

How do greenhouses or huge plastic polytunnels increase the yield of a crop?

Answer 44

The glass or plastic building means that the environment is much more controllable than in an ordinary garden or field. This means that farmers can try and eliminate limiting factors as much as possible:
*The temperature is maintained at the optimum temperature for enzyme activity
*Carbon dioxide levels are increased so they do not become a limiting factor
*Artificial lighting can be used to extend the hours of the day, and months of the year when plants can photosynthesise
*Plants can be grown in a mineral solution with a perfect balance of nutrients, such as nitrate ions, instead of soil to ensure optimum growth. This is called hydroponics
This increases the rate of photosynthesis and therefore the rate of growth of the plants.

Question 45

What is hydroponics?

Answer 45

Hydroponics is when soil is replaced by a mineral solution pumped around the plant roots instead of soil. Removing the soil means there’s no risk of soil organisms causing disease. Monitoring and adjusting the concentrations of minerals in the solution enable the farmer to optimise growth. Hydroponics allows crops to be grown in regions where there’s infertile or poor soil. Due to the costs involved, hydroponics is used only for high-value crops.

Question 46

Explain the economics of using a greenhouse to optimise photosynthesis:

Answer 46

Using a greenhouse and keeping the conditions just right can be very costly. Electricity and gas are used to maintain the lighting and temperatures and to control the carbon dioxide levels. Expensive monitoring systems are needed to maintain the conditions within the greenhouse. However, less staff are needed as much of it is automated, the time from seed to harvest is much shorter, and the final crop is larger and cleaner. The higher yields also help to increase profits

Question 47

In which cell organelle does photosynthesis take place?

Answer 47

Chloroplasts

Question 48

Which chemical in the leaves is required for photosynthesis?

Answer 48

Chlorophyll

Question 49

What is the compensation point in a plant?

Answer 49

When the rate of photosynthesis is equal to the rate of respiration

Question 50

In which layer of the leaf does the most photosynthesis take place?

Answer 50

Palisade mesophyll layer

Question 51

Where is starch stored in a plant?

Answer 51

Starch is the main energy store in plants and it is found in cells all over a plant:

• Starch is often stored in the cells of the leaves. It provides an energy store for when it is dark or when light levels are low
• Starch is also kept in special storage areas of a plant. For example, many plants produce tubers and bulbs that are full of stored starch to help them survive through the winter