Unit 2: Nutrition and transport in plants

Question 1

What is autotrophic nutrition?

Answer 1

• Simple compounds (inorganic substances (in plants this could be CO2, water, and light)) are absorbed and assimilated into complex substances, which are then oxidised (broken down) to release energy.
• Green plants are autotrophic (chlorophyll is necessary for this process)
• Plants > photosynthesis

Question 2

What is heterotrophic nutrition?

Answer 2

• Food is obtained directly from autotrophs
• Complex substances are broken down and are further oxidised or absorbed as nutrients

Question 3

Define photosynthesis

Answer 3

The process by which
plants manufacture carbohydrates from raw
materials using energy from light

Question 4

State the word equation for photosynthesis:

Answer 4

carbon dioxide + water → glucose + oxygen,
in the presence of light and chlorophyll

Question 5

State the balanced equation for photosynthesis

Answer 5

light
6(CO2) + 6(H2O)—————> C6H12O6 + 6(O2)
chlorophyll

Question 6

How do plants capture light and use it to make the substances it needs?

Answer 6

Certain plant cells contain chloroplasts. These contain a green pigment called chlorophyll. Light energy from sunlight is absorbed in these. It then releases this energy. The released energy makes CO2 combine with water, with the help of enzymes inside the chloroplast. The carbohydrate glucose is formed.
So the light energy has been converted into chemical energy for the synthesis of carbohydrates (stored in glucose)

Question 7

How are plants adapted for photosynthesis?

Answer 7

1. Large surface area for leaves: This allows
   plants to absorb more light and CO2.
2. Thin leaves: Light does not have to travel far to
   reach chloroplasts. Short distance for the
   diffusion of CO2.
3. Stomata in lower epidermis: Allow CO2 to
   diffuse into leaf and O2 to diffuse out of leaf.
4. Air spaces in spongy mesophyll: To allow CO2
   and O2 to diffuse to and from all cells.
5. Xylem and phloem vessels are close to the
   mesophyll cells: This allows water to be
   supplied to the cells and the products of
   photosynthesis to be removed.
6. Supported by stem and leaf stalks: Hold leaves out so that
   maximum CO2 and light can be absorbed.
7. Large surface area of root hair cells: Allows
   plants to take in as much water as possible by
   osmosis.
8. No chloroplasts in epidermis cells: to allow
   sunlight to penetrate to the mesophyll layer
9. Chloroplasts containing chlorophyll in the
   mesophyll layer: to absorb light energy for
   photosynthesis
10. Palisade cells arranged end on: To keep as
    few cell walls between sunlight and
    chloroplasts
11. Chloroplasts arranged on the broadside of
    palisade mesophyll cells: To expose as much
    chlorophyll to sunlight.
12. Chlorophyll arranged on flat membranes
    inside chloroplasts: To expose as much
    chlorophyll to sunlight.

Question 8

How is the glucose which is made in photosynthesis, used in the plant?

Answer 8

1. Some if it is used to immediately meet the energy needs of the plant through respiration
2. It could be converted into startch for storage
3. If it is being transported around the plant then it is converted into sucrose since that is less reactive and will not cause unwanted reactions to occur
4. Sucrose is used for growth of fruits or stored in fruits
5. Sucrose is used for growth of shoots and young leaves

Question 9

Draw out the structure of a leaf:

Answer 9

Question 10

What is the function of chloroplasts?

Answer 10

Contain chlorophyll to capture light

Question 11

What is the function of the waxy cuticle?

Answer 11

Stops water from evaporating from the leaf. Its transparency allows light to pass through it. Secreted by the upper epidermis.

Question 12

What is the function of the gaurdcells?

Answer 12

Open or close the stomata to allow diffusion: contain chloroplasts

Question 13

What is the function of the stomata?

Answer 13

Small openings on the underside of the leaf that allow diffusion of gases in and out of the leaf

Question 14

What is the function of the upper and lower epidermis?

Answer 14

Thin layers of cells that protect the inner cells and do not contain chloroplasts (Note: the lower epidermis contains guard cells, which DO contain chloroplasts). Upper epidermis Supports leaf when cells are turgid

Question 15

What is the function of the palisade mesophyll layer?

Answer 15

Contains closely packed cells which have chloroplasts

Question 16

What is the function of the spongy mesophyll layer?

Answer 16

Cells are loosely packed in this layer to allow diffusion of gases into and out of the leaf. Contains few chloroplasts but not as many as in the palisade mesophyll.

Question 17

What is the function of the vascular bundle?

Answer 17

Contains the xylem and phloem

Question 18

What is the function of the xylem?

Answer 18

Carries water from the roots to the leaves

Question 19

What is the function of the phloem?

Answer 19

Carries sucrose away from the leaves

Question 20

How are mineral ions transported through root hair cells?

Answer 20

Active transport

Question 21

What is the importance of nitrate ions in plants?

Answer 21

These contain nitrogen, a vital compound in the synthesis of amino acids. These create proteins.

Question 22

What is the importance of magnesium ions?

Answer 22

Magnesium ions are vital for the synthesis of chlorophyll. Without magnesium, photosynthesis cannot take place as the chloroplasts will not be able to absorb light energy from the Sun.

Question 23

Defiency of nitrate causes:

Answer 23

Poor growth ( coz no amino acids=no proteins) and yellow leaves. Weak stem
Leaves die
Bottom leaves yellow while leaves at the top turn pale green

Question 24

Magnesium deficiency causes:

Answer 24

Yellowing between the veins of the leaves through a process known as chlorosis. And cannot photosynthesize

Question 25

Phosphate in plants is a:

A deficiency of it causes:

Answer 25

1. A component of DNA and cell membranes.
2. Poor root growth and discoloured leaves

Question 26

Potassium in leaves is a:

A deficiency in it causes:

Answer 26

1. A component that must be present for photosynthesis and respiration enzymes to work.
2. Poor flower and fruit growth and discoloured leaves

Question 27

What is the xylem responsible for?

Answer 27

• Transporting water from the leaves up the stem and to the leaves
• Supporting the plant and keeping it upright. The walls of the xylem are made of lignin which is very strong.

Question 28

Structure of the xylem:

Answer 28

Cell walls thickened with lignin (polymer).
Composed of elongated dead cells.
Walls are Impermeable to water.
Has a one-way flow for transportation from roots to other parts of the plant.
Xylem vessels contain no cytoplasm or nuclei.
The walls are also made of cellulose.
End walls of cels have completely broken down.

Question 29

What is the phloem responsible for?

Answer 29

Transporting sugars and amino acids through the plant

Question 30

Structure of the phloem:

Answer 30

Includes cross wall perforations called sieve plates which separate adjacent cells, control flow by applying resistance and contains many pores through which nutrients pass through.
Composed of living cells that are dependent on companion cells containing organelles needed to make it a living cell, making space for molecules to pass through. Phloem employ active transport which requires energy, provided by the companion cells.
Permeable cell walls.
Has a two-way flow for transportation up and down for all parts of the plant. This is called translocation - the transportation between where these substances are made (sources) and used up or stored (sink).
Phloem contain cytoplasm but no nucleus.

Question 31

What is active transport?

Answer 31

the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration.

Question 32

What is the structure of stemm in plants:

Answer 32

Question 33

Draw and label the structure of plant roots.

Answer 33

g

Question 34

What is a vascular bundle? What is its role?

Answer 34

A strand of conducting vessels composed of the xylem and phloem. The position of the vascular bundles vary in different parts of the plant.

Root - Found in the centre of the root in order to resist forces that could pull the plant out of the ground.
Stem - Arranged near the edge of the stem to resist compression and bending forces caused by factors such as the weight of the plant and the wind.

The lignified walls of the xylem provide the support mentioned above.

Question 35

Draw and label a cross-section of a plant leaf (with the phloem and xylem)

Answer 35

Question 36

What is the structure of the root of a plant?

Answer 36

At the very tip is the root cap - this is a layer of cells which protects the root as it grows through the soil. The rest of the root is covered by a layer of cells called the epidermis. The root hairs are a little way up from the root tip. Each root hair is a long epidermal cell.

Question 37

What does the large surface area of root hair cells do?

Answer 37

This increases the area available for the absorption of water and ions. Water is absorbed by osmosis, while ions are absorbed by active transport. The root hairs increase the rate of absorption of water and ions.

Question 38

Describe the path water takes up a plant:

Answer 38

1. Water moves into the plant by osmosis into root hair cells - down its concentration gradient through the partially permeable cell membranes. 2. Through osmosis, it passes from cell to cell through the root cortex cells. Some of the water may also just seep through the spaces between the cells, or through the cell walls, never actually entering a cell at all.
2. Eventually, it reaches the xylem vessels in the middle of the root. The xylem carries the water through the stem into the mesophyll cells (remember that in leaves vascular bundles are known as “veins” which enter the mesophyll layer). The reason why the water goes up the xylem is that the pressure at the top of the vessels is lowered (because of transpiration), while the pressure at the bottom stays high. The water molecules will therefore move from a higher to lower pressure and up the xylem vessels. This is known as “mass flow”.
3. Another reason why water goes up the xylem is capillary Action (Adhesion) - The attraction between the water molecules and the walls of the xylem vessels which causes an upward flow on liquid around edges.

(also remember that the water contains dissolved minerals)

(Something else to note: Capillary action helps bring water up into the roots. But capillary action can only “pull” water up a small distance, after which it cannot overcome gravity. To get water up to all the branches and leaves, the forces of adhesion and cohesion go to work in the plant’s xylem to move water to the furthest leaf.)

Question 39

Define transpiration

Answer 39

The loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata.

Question 40

Describe the process of transpiration:

Answer 40

• Water leaves the plant by transpiration through the leaves.
• This reduces the pressure at the top of the xylem vessels.
• This creates a ‘transpiration pull’: water molecules are drawn up through the xylem as they move towards the area of lower water potential at the top of the plant.
• One of the properties of water is that the molecules want to stick together. This cohesion means that a column of water is drawn up the stem of the plant.
• The water in the mesophyll cells forms a thin layer on the surface of the cells. This water evaporates into the air spaces of the spongy mesophyll layer. This increases the concentration of water molecules in these air spaces. As a result, the water vapour diffuses out of the leaf: it moves to an area where the concentration of water molecules is lower. This reduces the water potential inside the leaf (the holes/gaps between the spongy cells have a lowered water potential), causing more water to evaporate from the surfaces of the mesophyll cells (into the holes.gaps).

Question 41

How is the structure of a plant adapted to help it take up more water and move it up the plant?

Answer 41

1. Root hair = large surface area = increases the amount of water that can move into the plant at any one moment.
2. Xylem vessels = hollow & narrow = easy pathway for water to follow
3. Many air spaces in leaf = large surface area of wet cells from which water can evaporate into the air = increases rate of evaporation = speeds up flow of water up the plant
4. The stomata, when open, allow water vapour to diffuse easily out of the leaf.

Question 42

What are the factors that affect transpiration rate?

Answer 42

temperature
humidity
wind speed
light intensity
water supply

Question 43

Why does each factor affect transpiration rate and how?

Answer 43

Temperature:
Increase in temperature = water molecules have more kinetic energy = diffuse faster = transpiration rate increases

Humidity:
Increase in humidity = increase in moisture content of air = weakens water-potential/diffusion gradient = transpiration rate decreases

Wind speed/Air movement:
Removes water vapour from leaf surfaces = steepens water potential gradient = more water diffuses from the leaf

Light intensity:
Increases the rate of photosynthesis; stomata open so more water diffuses out of the leaf, The stomata open wider to allow more carbon dioxide into the leaf for photosynthesis.

Question 44

(syllabus statement) Explain the mechanism by which water moves up…

Answer 44

water moves upwards in the xylem in terms coz of transpiration pull, helping to create a water potential gradient that draws up a column of water molecules, held together by cohesion

Question 45

Define translocation:

Answer 45

The movement of sucrose and amino acids in phloem:
– from regions of production (source)
– to regions of storage OR to regions where
they are used in respiration or growth (sink)

Question 46

Examples of sources and sinks:

Answer 46

Sources: Leaves

Sinks: Roots, the stem, flowers, fruits, seeds.

Some parts of a plant may act as both a source and a sink at different times. For example, the leafy parts of many plants cannot survive the cold winter months. These plants will store sucrose in parts of the plant underground during the winter; this sucrose is stored as starch. In spring, when the plant begins to grow again, the starch is converted back to sucrose and transported to the growing stem and the leaves. As the plant begins to grow, the leaves are now the sink.

Question 47

Explain how translocation happens:

Answer 47

The source cell (leaf) loads sucrose into the phloem (phloem loading). This is done through active transport. Some leaves have the enzyme required to create ATP for this called a tonoplast. The solute concentration increases lowering water potential in comparison to the xylem. Water from the xylem enters the phloem (osmosis). This increases the cellular contents in the phloem and puts more pressure on the walls. The contents get pushed down to an area of lower pressure. (Sap moves from a place of higher concentration to lower concentration). As the sap enters the sink the water potential in the phloem then increases and water moves into the xylem (osmosis).

Question 48

Does the waxy cuticle stop transpiration from other parts of the leaf other than the stomata?

Answer 48

Yes

Question 49

Describe the process of eutrophication:

Answer 49

• Farmers use fertilisers to ensure their crops are provided with the right nutrients.
• Since they are soluble they get washed away by the rain into a nearby lake/pond/river system.
• Algae in the system feed on this, growing & reproducing rapidly. This creates an algal bloom on the surface. All sunlight is absorbed by this and blocked out for plants at the bottom of the lake/river/pond.
• Once the algae have consumed all nutrients they start to die off.
• Bacteria break up the dead algae and plants, continuing the algal bloom cycle.
• As the bacteria population in the system grows - they consume more and more of the oxygen.
• Water without oxygen is anoxic, all non-bacterial organisms including fish die.

Question 50

Explain how guard cells work:

Answer 50

During the day = photosynthesis = higher concentration of solutes in guard cell = hypertonic = absorbs water (osmosis) = becomes turgid = during the night it will operate oppositely.

During the day = want to reduce water loss through transpiration coz the stoma open to allow CO2 in for photosynthesis.

During the night = want to absorb CO2

Question 51

What is a limiting factor?

Answer 51

•the thing which stops photosynthesis from happening any faster •e.g light intensity, co2 conc., temperature •depends on enviromental conditions, e.g in winter will probably be temperature, at night will probably be light.

Question 52

How would the number of stomata affect rate of transpiration?

Answer 52

More stomata = faster rate of transpiration;
as there are more routes or water to leave the leaf;

Question 53

How would the the number of air spaces in a plant affect the rate of transpiration?

Answer 53

More air spaces leads to faster rate of transpiration;
as there is more air surround spongy mesophyll cells;
leading to more evaporation;

Question 54

Give an example of translocation:

Answer 54

flow from storage organs, like potatoes;
back to the stem and growing areas of the plant when required;

Question 55

What are the limiting factors of photosynthesis?

Answer 55

1. Light
2. CO2
3. Temperature

Question 56

How is light a limiting factor of photosynthesis?

Answer 56

As light intensity increases so does photosynthesis - up to a certain point where it levels off. This is because the plant is unable to acquire enough CO2 to react with the light.

Graph link: https://drive.google.com/drive/u/0/folders/1DtmZWjU9PbXfbASTaOWSiegGl9DoBpRp

Question 57

How is CO2 a limiting factor of photosynthesis?

Answer 57

At one point it will saturate the enzymes and they won’t be able to function.

Graph link: https://drive.google.com/drive/u/0/folders/19Rl5SPLWQ0M9WS-Q5midQpByaUG6ZAqP

Question 58

How is temperature a limiting factor of photosynthesis?

Answer 58

At one point when the enzymes overheat, they will de-nature.

Graph link: https://drive.google.com/drive/u/0/folders/1ziK8l8slHTVgDKW57aULvY17WJU_ZJIl

Question 59

Why do the veins in a leaf branch repeatedly?

Answer 59

Veins are spread all over the leaves ,so they can easily transport water to all the cells of leaves.

Question 60

Why is starch used for storage in plants?

Answer 60

Starch is insoluble in water so won’t affect the way water moves in and out of the plant, meaning plants can store large amounts of starch in their cells. Starch molecules are very large so they cannot move out of the cell. This means they can act as energy stores.

Question 61

Answer 61

Question 62

What is the difference between cohesion and adhesion of water molecules?

Answer 62

Adhesion is generally the force of attraction present between the water molecules and the walls of xylem vessels. Cohesion force is unrestrained among water molecules.

Cohesion: Water is attracted to water, and Adhesion: Water is attracted to other substances.