Biology - Plants and photosynthesis

Question 1

What is photosynthesis?

Answer 1

A chemical process used by plants to make water from the soil into glucose and carbon dioxide from the air into oxygen using light energy. Oxygen is produced as a by-product of photosynthesis.

Question 2

What is the equation to summarise photosynthesis?

Answer 2

Carbon dioxide + Water → Glucose + oxygen.
(Above the arrow light - Below he arrow chlorophyll)

Question 3

How does temperature effect photosynthesis?

Answer 3

Photosynthesis is controlled by enzymes, which become denatured if the temperature is too high. As a result, the rate of photosynthesis reaches its maximum at an optimum temperature, then decreases. The maximum rate is determined by the other factors involved.

Question 4

How does light intensity effect photosynthesis?

Answer 4

Light provides the energy needed for photosynthesis. Increasing the light intensity increases the rate of photosynthesis, provided plenty of carbon dioxide and water are available. The maximum rate is determined by the other factors involved.

Question 5

What is an experiment to test light intensity?

Answer 5

In this experiment, a light is moved further from a photosynthesising plant to vary the light intensity the plant receives. The further the light moves from the plant, the fewer oxygen bubbles are produced by photosynthesis.

Question 6

How does carbon dioxide effect photosynthesis?

Answer 6

Increasing the carbon dioxide concentration increases the rate of photosynthesis, provided the plant is warm enough, and has plenty of light and water. The maximum rate is determined by the other factors involved.

Question 7

How do you test a leaf for starch?

Answer 7

-Heat a plant leaf in boiling water for 30 seconds (this kills the leaf, stopping any chemical reactions)
-Add the leaf to boiling ethanol in a water bath for a few minutes (the boiling ethanol dissolves the chlorophyll and removes the green colour from the leaf - it turns white so it is easy to see the change in colour)
-Wash with water to rehydrate and soften the leaf and spread onto a white tile
add iodine solution from a dropping pipette.

After a few minutes, the parts of the leaf that contain starch turn the iodine from brown to blue/black.

Question 8

How is starch tested on a variegated leaf showing the importance of chlorophyll in photosynthesis?

Answer 8

Variegated leaves have green parts (where the cells contain chlorophyll) and white parts (where there is no chlorophyll). Only the parts that were green become blue/black with iodine solution, showing the importance of chlorophyll in photosynthesis. Chlorophyll photosynthesises to make starch.

Question 9

How can a leaf be de-starched showing the importance of light in photosynthesis?

Answer 9

A plant can be ‘de-starched’ by leaving it in the dark for a few hours. Parts of its leaves are covered with dark paper, and the plant is left in the light for a few hours. Only the uncovered parts become blue/black with iodine solution, showing the importance of light in photosynthesis.

Question 10

How do you test if a plant needs carbon dioxide for photosynthesis?

Answer 10

In this particular experiment, a de-starched plant is covered using an airtight transparent plastic bag. The chemical sodium hydroxide is placed in the bag with the plant to absorb the carbon dioxide. The plant is left for 24 hours and the leaves are tested for starch using iodine. The leaves will show that no starch has been made as no photosynthesis occurred without carbon dioxide.

Question 11

Where does light absorption happen in the plant cell?

Answer 11

Light absorption happens in the palisade mesophyll tissue of the leaf. Palisade cells are column-shaped and packed with many chloroplasts. They are arranged closely together so that a lot of light energy can be absorbed.

Question 12

What are the adaptions of leaves and their functions

Answer 12

Large surface area - maximise light absorption.
Thin - Short distance for carbon dioxide to diffuse into leaf cells
Cuticle - A waxy waterproof layer which reduces water loss, it is transparent to allow light through the leaf

Question 13

What is the role of the stomata?

Answer 13

The stomata control gas exchange in the leaf. Each stoma can be open or closed, depending on how turgid its guard cells are. The stomata can open and close to:
regulate transpiration, allow gas exchange

Question 14

What does the xylem do?

Answer 14

Xylem transports water and mineral salts from the roots up to other parts of the plant.

Question 15

What does the phloem do?

Answer 15

Phloem transports sucrose and amino acids from the leaves and other parts of the plant.

Question 16

What is transported by the xylem and phloem?

Answer 16

Xylem - Water and minerals via transpiration stream
Phloem - Sucrose and amino acids via translocation

Question 17

What are the properties of a mature xylem vessel?

Answer 17

-Contain no cytoplasm
-Are impermeable to water
-Have tough walls containing a woody material called lignin

Question 18

Where are the vascular bundles in the root?

Answer 18

Xylem vessels are tough and strong, so the vascular bundles are in the centre of the root to resist forces that could pull the plant out of the ground.

Question 19

Where are the vascular bundles in the stem?

Answer 19

The stem has to resist compression (squashing) and bending forces caused by the plant’s weight and the wind. The vascular bundles are arranged near the edge of the stem, with the phloem on the outside and the xylem on the inside.

Question 20

What are vascular bundles?

Answer 20

Groups of xylem and phloem tissue on a plant.

Question 21

What is transpiration?

Answer 21

The loss of water from leaves by evaporation through the stomata.

Question 22

What is a transpiration stream?

Answer 22

The flow of water in the xylem from the roots to the leaves.

Question 23

How does water move up the plant?

Answer 23

Transpiration produces a tension or ‘pull’ on the water in the xylem vessels by the leaves. Water molecules are cohesive so water is pulled up through the plant.

Question 24

What functions does a transpiration stream have?

Answer 24

-Transporting mineral ions
-Providing water to keep cells turgid by filling vacuoles in order to support the plant and stop it wilting
-Providing water to leaf cells for photosynthesis
-Keeping the leaves cool by evaporation

Question 25

What is the purpose of the root hair cell?

Answer 25

The root hair cells are where most water absorption happens.

Question 26

How are root hair cells adapted for absorption?

Answer 26

They are long and thin so they can penetrate between soil particles, and they have a large surface area for absorption of water through osmosis.

Question 27

How can the decrease in mass of a plant due to transpiration be investigated?

Answer 27

-Select four leaves of similar size.
-Cover the surfaces of the leaves with petroleum jelly differently. (No jelly, top side covered, bottom side covered, both sides covered)
-Record the initial mass of the leaves.
-After 24 hours record the mass of the leaves and calculate the percentage decrease in mass.

Question 28

What conclusions can you make from the results of the petroleum jelly experiment?

Answer 28

You can conclude that most transpiration happens from the lower surface of the leaf:

coating the upper surface caused water loss similar to coating no surface at all
coating the lower surface caused water loss similar to coating both surfaces

Question 29

What is a potometer?

Answer 29

A potometer can be used to measure the rate of transpiration that’s proportional to water uptake.

Question 30

What is the method of the experiment involving a potometer?

Answer 30

-A single air bubble is introduced into the capillary tubing.
-The tap on the reservoir is opened to add water to push the air bubble back to zero on the scale.
-A timer is started and a set time measured.
-The distance the air bubble has travelled along the scale is recorded.
-The experiment can be repeated with different environmental conditions.

The faster the bubble moves, the greater the rate of water uptake – and so the greater the rate of transpiration.

Question 31

What are some factors that may effect the rate of transpiration?

Answer 31

-Temperature - Increased - Evaporation and diffusion are faster at higher temperatures.

-Humidity - Decreased - Humidity decreases the concentration gradient between the inside and outside of the leaf – this reduces transpiration

-Wind speed - Increased - Moving air removes water vapour, increasing the rate of diffusion of water vapour from the leaf

-Light intensity - Increased - The stomata open wider to allow more carbon dioxide into the leaf for photosynthesis

Question 32

What are the three minerals needed for plant growth and why are they needed?

Answer 32

-Nitrates - Nitrogen, N - Nitrogen is needed to make amino acids for proteins, which are needed for cell growth.

-Phosphates - Phosphorus, P - Phosphorus is needed to make DNA and cell membranes

-Potassium compounds - Potassium, K - Potassium is needed in enzymes involved in respiration and photosynthesis.

Question 33

What three minerals cause mineral deficiencies and what are the symptoms?

Answer 33

Nitrate - Poor growth
Phosphate - Poor root growth
Potassium - Yellowing of leaves

Question 34

How are minerals absorbed?

Answer 34

Through active transport. The root hair cells have carrier proteins in their cell membranes. These pick up the mineral ions and move them across the membrane into the cell against the concentration gradient.