Plants and Food

Question 1

How can you prevent a plant from making starch?

Answer 1

Deprive it from light OR put it in a closed container containing soda like which absorbs all the carbon dioxide in the air.

Question 2

What is the main storage carbohydrate made by plants?

Answer 2

Starch

Question 3

How can you show that plants produce oxygen in light?

Answer 3

Use an aquatic plant and place a piece of this plant, for example elodea, in a test tube under bright light. It will produce a stream of bubbles. Collect these and test their contents for oxygen. They should contain a high concentration of oxygen.

Question 4

How do plants make starch?

Answer 4

Starch is composed of long chains of glucose. A plant first makes glucose, which is then joined together in chains to make starch molecules.

Question 5

Word equation for photosynthesis:

Answer 5

Carbon dioxide + water —> glucose + oxygen (Light and chlorophyll on the arrow)

Question 6

What is the role of the chlorophyll?

Answer 6

It is a green pigment that absorbs all the light energy needed to take place.

Question 7

What does photosynthesis do?

Answer 7

Converts light energy into chemical energy.

Question 8

Chemical equation for photosynthesis:

Answer 8

6H20 + 6C02 —> C6H12O6 + 6O2

Question 9

Why is photosynthesis important? (2)

Answer 9

Because it allows plants to make glucose (food)

Because it produces oxygen for all animals and plants that respire aerobically

Question 10

What type of nutrition is photosynthesis?

Answer 10

Autotrophic

Question 11

What does respiration do?

Answer 11

Releases energy from the breakdown of glucose. This chemical energy came originally from the light ‘trapped’ by the process of photosynthesis.

Question 12

What do leaves need to be able to photosynthesise efficiently?

Answer 12

1) Large surface area to absorb light. 2) many chloroplasts containing chlorophyll 3) a supply of water and carbon dioxide 4) a system for carrying away the products of photosynthesis to other parts of the plant

Question 13

What are the outer layers of cells of a leaf and what are their functions?

Answer 13

The outer layers of cells are the upper and lower epidermis which have few chloroplasts and are covered by a thin layer of wavy material called the cuticle. This reduces water loss by evaporation and acts as a barrier to the entry of disease causing microorganisms so such as bacteria and fungi.

They are also transparent which allows light to pass through the epidermis to the chloroplasts in the palisade layer

Question 14

Where are the stomata found and what are their function?

Answer 14

In the lower epidermis there are many pores called stomata (one stoma). These allow carbon dioxide to diffuse into the leaf, to reach photosynthetic tissues. They also allow oxygen and water vapour to diffuse out.

Question 15

What is a stoma?

Answer 15

Each stoma is formed as a gap between two highly specialised cells called guard cells. The guard cells can alter their shape to open or close the stoma.

Question 16

Where is the palisade layer found and what is its function?

Answer 16

Just below the upper epidermis is a palisade layer made from elongated cells, each containing hundreds of densly packed chloroplasts which absorb light and is the main site of photosynthesis. They are close to the source of light and the upper epidermis is relatively transparent allowing light to pass though.

Question 17

What is below the palisade cells? What is its function?

Answer 17

The spongy mesophyll layer. These cells also photosynthesise but have less chloroplasts that the palisade cells. They form the main gas exchange surface of the leaf, absorbing carbon dioxide and releasing oxygen and water vapour.

Question 18

Why do the spongy mesophyll have air spaces?

Answer 18

To allow oxygen, carbon dioxide and water vapour to diffuse in and out of the mesophyll.

Question 19

What is a gas exchange surface?

Answer 19

A tissue that allows gases (usually oxygen, carbon dioxide and water vapour) to pass across it between the plant or animal and the outer environment. They have a large surface area to volume ratio which allows large amounts of gases to diffuse across.

Question 20

How are water and mineral ions supplied to the leaf?

Answer 20

By vessels in a tissue called the xylem. This forms a continuous transport system throughout the plant. Water is absorbed by the roots and passes up though the stem and though veins in the leaves in the transpiration stream. In the leaves, water leaves the xylem and supples the mesophyll cells.

Question 21

How are the products of photosynthesis carried in the leaf?

Answer 21

They are carried away from the mesophyll cells by the phloem. This supplies all other parts of the plant so that the tissues and organs that can’t make their own food receive the products of photosynthesis.

Question 22

When will a plant produce more carbo dioxide than it uses?

Answer 22

In dim light as it cannot carry out carbon dioxide efficiently but it continues to produce carbon dioxide as a product of respiration.

Question 23

How does the concentration of carbon dioxide in the air change throughout the day?

Answer 23

It is an upside down bell curve with the lowest point being noon.

Question 24

Why is the concentration of carbon dioxide around a plant different at different times of day?

Answer 24

At noon the sun will be directly above the plant and photosynthesis will be happening at its highest rate meaning carbon dioxide is used up faster. At night when there is no photosynthesis as there is no light, the level of carbon dioxide rises. This is because whilst no carbon dioxide is being absorbed by plants. It is still added to the air by respiration of all the organisms in the area.

Question 25

What do plants you glucose for?

Answer 25

In a plant glucose is converted into:

• starch for storage
• other sugars like fructose or sucrose which is the main sugar carried in the phloem
• the polymer cellulose, which forms plant cell walls
• lipids for the membrane of all cells and an energy store in seeds and fruits
• proteins and DNA (when mineral ions from soil is added)
• chlorophyll (when magnesium ion for soil is added)

Question 26

How can glucose be used for so many things?

Answer 26

Carbohydrates and lipids both contain only 3 elements - carbon, hydrogen and oxygen. This means they can be inter-converted without the need for a supply of other elements.

Proteins contain these elements too, but all amino acids contain nitrogen as well which is why nitrate ions are obtained through a plants roots.

Question 27

Why do plants need mineral ions and how do they get them?

Answer 27

For healthy growth and they are absorbed through the roots as the mineral ions are dissolved in the soil water

Question 28

What two important mineral ions do plants need?

Answer 28

Magnesium and Nitrate

Question 29

Why do plants need nitrate ions?

Answer 29

To make amino acids, which are needed to make proteins and needed for the growth of new cells.

Also needed to make chlorophyll, DNA and many other compounds.

Question 30

Why do plants need magnesium ions?

Answer 30

To make chlorophyll

Question 31

Why do plants need potassium ions?

Answer 31

For enzymes of respiration and photosynthesis to work

Question 32

Why do plants need phosphate ions?

Answer 32

making DNA and many other compounds, part of cell membranes

Question 33

How does varying light intensity affect the rate of photosynthesis?

Answer 33

With insufficient light, a plant can not photosynthesise very quickly, even if there is water and co2 Increasing the light intensity will increase the rate of photosynthesis

Question 34

How does varying carbon dioxide concentration affect the rate of photosynthesis?

Answer 34

The rate of photosynthesis increases if there is a higher carbon dioxide concentration and if there is insufficient carbon dioxide a plant cannot photosynthesise

Question 35

How does temperature affect the rate of photosynthesis?

Answer 35

If the temperature is too cold, the rate of photosynthesis will decrease Plants cannot photosynthesise if it is too hot. There is an ideal temperature when photosynthesis is best (the graph is a sad face)

Question 36

What is the main Storage carbohydrate made by plants?

Answer 36

Starch

Question 37

How do you test for starch?

Answer 37

Add a few drops of the iodine solution, it the colour turns blue/black there is starch present. If not it is orangey yellow.

Question 38

Why can you not test for starch on a new fresh leaf?

Answer 38

The outer waxy surface layer will not absorb the solution and the green colour will hide the colour change.

Question 39

What must you do before you place the iodine solution on the leaf when testing for starch?

Answer 39

The leaf must be decolorised and the outer waxy layer must be removed. This is done by placing the leaf in boiling ethanol.

Question 40

Give an example of an experiment to show that starch is only produced in the parts of plants that are green.

Answer 40

Test the starch on a VARIAGATED leaf and you will see that the white regions that don’t contain chlorophyll are my positive for starch.

Question 41

What must you take caution with when heating ethanol?

Answer 41

Do not heat the tube directly but in a beaker filled with water as ethanol is highly flammable.

Question 42

Write a method for the rest of starch in a leaf.

Answer 42

A beaker of water is set up on a tripod and the water is heated until it boils. A leaf is removed from a plant and killed by placing it in the water for 30 seconds. (This stops all chemical reactions in the leaf). The Bunsen burner is turned off, the leaf placed in a boiling tube containing ethanol, and the tube stood in the beaker of hot water. B.P. of ethanol is lower than that of water to it will boil for a few minutes until the water cools down. Long enough to remove most of the chlorophyll from the leaf. When the leaf has turned colourless it is removed and washed in cold water then spread out on a tile and covered with a few drops of iodine and after a few minutes any parts of the leaf that contained starch will turn blue or black.

Question 43

How can you show that plants produce oxygen when in light?

Answer 43

Place an aquatic plant (elodea) in a test tube of water under a bright light. It produces a stream of small bubbles. If the bubbles are collected and their contents analysed, they are found to contain a high concentration of oxygen.

Question 44

Give an experiment to show that carbon dioxide is needed in photosynthesis?

Answer 44

A plant is surrounded with a glass bell jar and inside it is soda lime. There is light on the plant but the soda lime absorbs the carbon dioxide from the air in the bell jar. A control experiment should be set up wih the exact same apparatus but without the soda lime or with sodium hydrocarbonate to provide CO2. Comment on the effect of the plant without CO2.

Question 45

What is the role of chlorophyll?

Answer 45

To absorb the light energy needed for photosynthesis to take place.

Question 46

What would you use to indicate change in CO2 levels?

Answer 46

Hydrocarbonate indicator solution.

Question 47

What are the colour changes with Hydrocarbonate indicator solution?

Answer 47

High conc. = yellow Normal air conc. = orange Low conc. = purple

Question 48

Give an experiment to investigate the effect of light on photosynthesis.

Answer 48

10cm3 of hydrocarbonate indicator solution is placed in the bottom of four boiling tubes. Three large leaves are placed at the top of each tube and they are sealed with a bung. One is the control so there is no leaf. One tube is in light, one in the dark covered with silver foil, one dim light and in the control light.

Question 49

What would the colour of the Hydrocarbonate indicator solution be at the end of this experiment for the four tubes?

Answer 49

The leaf in light would be purple (low CO2) Leaf in dark would be yellow (high CO2) Leaf in dim would be orange as well as control (normal CO2).

Question 50

Explain the conc. of CO2 in this experiment (the four test tube leaf one)

Answer 50

The leaf in the light would be respiring and photosynthesising but photosynthesis would be happening at a faster rate so more CO2 would be used up and there would be a lower conc. in the test tube. The leaf in the dark would be respiring at a faster rate than photosynthesising because there is no light so photosynthesis would not happen. This means there would be a high conc of CO2 as it is produces but not used up. Dim light means respiration and Photosynthesis are happening at a similar rate so the CO2 level is normal.

Question 51

Why does increased oxygen in soil help plants to grow

Answer 51

Oxygen is used in respiration. The energy released in respiration helps the roots carry out active transport so that mineral ions can enter the plant

Question 52

Explain how less plants can help the plants that are there grow

Answer 52

Less plants reduced competition for eg mineral ions and light

Question 53

Why do plants absorb any other colour light better than green light?

Answer 53

Because chlorophyll in plants is green so it reflects the green light more.

Question 54

How are the stomata adapted for gas exchange?