B7.1 Structure of a plant and transpiration

Question 1

Structure of Dicotyledonous Plant Leaf

Answer 1

1. Leaves are made up of layers of different tissues, and also have xylem and phloem vessels running through them.
2. A waterproof, waxy cuticle covers the upper and lower epidermis.
3. Air spaces allow diffusion of gases through the spongy mesophyll.
4. Most photosynthesis happens in the palisade mesophyll cells.

Question 2

Leaf Anatomy

Answer 2

1. Cuticle
2. Epidermis
3. Guard cells
4. Mesophyll
5. Phloem
6. Xylem
7. Stomata

Question 3

Cuticle

Answer 3

1. the outer surface of the leaf has a thin waxy covering called the cuticle
2. its function is to prevent water loss within the leaf and provide waterproofing without reducing light absorption
3. The cuticle is a clear waxy layer that surrounds the leaf.

Question 4

Epidermis

Answer 4

1. directly underneath the cuticle is a layer of cells called the epidermis
2. the epidermis acts as a protective barrier around the leaf to prevent pathogens entering and causing harm to the organism.
3. Epidermis cells are transparent to let light pass through and do not contain chloroplasts.
4. lower epidermis and upper epidermis

Question 5

Veins of the leaf

Answer 5

1. location of the xylem and phloem

2. extensions that run from the tips of the roots all the way up to the edges of the leaves

Question 6

Mesophyll

Answer 6

1. layer of cells
2. the word mesophyll is greek and means “middle leaf”
3. Mesophyll can be divided into two layers, the palisade layer and the spongy layer

Question 7

Palisade mesophyll cells

Answer 7

1. these cells are positioned near the top of the leaf where most sunlight hits, thus palisade cells are adapted to absorb light energy efficiently.
2. The palisade layer cells contain many chloroplasts to carry out photosynthesis.
3. coloumn-like and arranged closely together and lie just under the epidermis

Question 8

Stomata

Answer 8

1. tiny holes within the epidermis
2. Stomata are gaps in the lower epidermis of leaves that facilitate (make easier) the diffusion of gases, including evaporated water, in and out of the leaf.
3. Guard cells can open and close the stomata
4. The stomata control gas exchange in the leaf.
5. Stoma open and close to regulate transpiration and allow gas exchange
6. Carbon dioxide enters the leaf through diffusion and behind each stomata is an air space which connects up with other air spaces between the spongy mesophyll cells. The carbon dioxide can therefore diffuse to all the cells in the leaf

Question 9

Opening the stomata

Answer 9

The guard cells can open the stomata by taking up lots of water, causing them to swell and bend away from each other, opening the stomata

Question 10

Closing the stomata

Answer 10

1. To close the stomata, the guard cells lose water and return to a limp state.
2. during dry times, the guard cells close

Question 11

Plant vessels

Answer 11

In dicotyledonous plants the veins (like the blood vessels of a plant) branch out through the leaf.

Question 12

Plant structure needs

Answer 12

1. a way to transport water to the leaf, and glucose to other parts of the plant
2. a way to exchange carbon dioxide and oxygen
3. the ability to absorb light energy efficiently

Question 13

xylem vessels

Answer 13

1. In plants, water and minerals like sodium are transported from the roots to the leaves through xylem vessels.
2. Xylem vessels are long, hollow, continuous tubes made of dead cells.
3. They have thick cell walls to support the plant and withstand the high pressure when transporting water. The walls are made of cellulose and lignin. Lignin is very strong so xylem vessels help support the plant and keep it upright
4. Direction of transport is up the stem (from the root to the leaf)
5. The process driving transport (across the membrane) is osmosis
6. Transpiration drives water movement trough the xylem tissue
7. vascular tissues
8. the end walls have disappeared, so a long open tube is formed
9. contain no cytoplasm or nuclei
10. pressure at the top of the vessels is lowered while the pressure at the bottom stays high so water flows up (transpiration is constantly removing water from the top of them thus reducing the pressure at the top)
11. water lost leads to wilting

Question 14

Vascular bundle

Answer 14

1. Xylem and phloem tissues are found in groups called vascular bundles.
2. The position of these bundles varies in different parts of the plant.
3. vascular bundles form the plant’s transport system.
4. form the veins in the leaf
5. contain tubes that carry substances to and from the leaf

Question 15

Vascular tissues

Answer 15

composed of organs that transport substances from one region to another region within an organism

Question 16

Root Hair cell.

Answer 16

1. Root hair cells are responsible for absorbing water and minerals from the soil
2. Root hair cells have a long projection called a root hair, that extends into the soil. This helps to increase the surface area for absorption of water and mineral ions.
3. at the end of the cell is a root cap which 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
4. They do not live very long and are replaced by new ones as the root grows
5. Water moves in through osmosis and mineral ions are taken up by active transport (low to high)into the root hair cells. It then moves cell to cell then moves to the root cortex cells then into the xylem vessels

Question 17

Phloem vessels

Answer 17

1. Phloem consists of living cells arranged end to end.
2. Unlike xylem, phloem vessels contain cytoplasm, and this goes through holes from one cell to the next.
3. Phloem transports sucrose and amino acids and water (which is a solvents
4. transports up and down the plant. (it is bidirectional)
5. The process driving transport (across the membrane) is facilitated diffusion: In general, this happens between where these substances are made (the sources) and where they are used or stored (the sinks).
6. vascular tissue
7. End walls have not completely broken down. The cells are called sieve tube elements which contain cytoplasm but no nucleus. Sieve tubes have small holes that allow food products to move up and down the phloem vessels throughout the plant. Sieve tubes are in phloem tubes which are made up of columns of elongated cells
8. They do not have lignin in their cell walls
9. transport of substances in the phloem requires energy. One or more companion cells attached to each sieve tube provide this energy. A sieve tube is completely dependent on its companion cell(s).
10. translocation drives movement trough the phloem tissue

Question 18

Position of vascular bundle in the root

Answer 18

1. 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.
2. xylem is inside (cross) while the phloem is outside

Question 19

Position of vascular bundle in the stem

Answer 19

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

Question 20

Position of vascular bundle in the leaf

Answer 20

1. xylem is on top and phloem is below of the vascular bundle

Question 21

Spongy Mesophyll layer

Answer 21

1. This is the lower layer of the leaf.
2. Cells are loosely spaced and have a large surface area for efficient gas exchange
3. air spaces allow for rapid diffusion of CO2, water and oxygen when the stomata are open.
4. packed with chloroplasts
5. Cells are rounder, and arranged quite loosely, with large air spaces between them
6. The spongy mesophyll cells are covered by a thin layer of water. Gases dissolve in this water as they move into and out of the cells.

Question 22

Upper epidermis

Answer 22

cells of the upper epidermis often secrete a waxy substance that lies on top of them called the cuticle

Question 23

Lower epidermis

Answer 23

1. there are small openings called stomata in the lower epidermis

Question 24

Leaf adaptations

Answer 24

1. leaf is broad and flat to obtain as much sunlight as possible
2. Leaves are arranged so they do not cut off light from one another more than necessary
3. Leaves are thin so sunlight is able to penetrate right through it to reach all the cells

Question 25

Translocation

Answer 25

1. Translocation is the movement of sucrose and amino acids from regions of production (source) to regions of storage or use in respiration (sink).

Question 26

Sources

Answer 26

Sources are areas of the plant which produce sugars e.g. leaves.

Question 27

Sinks

Answer 27

Sinks are areas of the plant which store or use sugars e.g. roots.

Question 28

Investigating the water pathway of water in a leaf

Answer 28

By putting a wilting celery stalk in water that contains a stain such as blue food dye, it is possible to watch the blue water travelling up the celery stem and to the leaves.

Question 29

Transpiration

Answer 29

1. Transpiration is the name given to the loss of water vapour from plant leaves.
2. Consequence of the opening of stomata
3. Water at the surfaces of the mesophyll cells evaporates and then diffuses (as water vapour) out of the stomata. (loss of water vapour)
4. most of the water is lost through transpiration

Question 30

Transpiration pull

Answer 30

1. Leaves: The loss of water from the mesophyll cells due to evaporation (transpiration), raises the water potential of the mesophyll cells. It reduces the effective pressure at the top of the xylem vessels so that water flows up them. Water is moved from the xylem to the mesophyll cells by osmosis.
2. Xylem: Water molecules show cohesion (tendency to stick together). As water molecules are pulled out of the xylem into the mesophyll, the whole column of water stays together creating a tension (or pull) at the top of the xylem vessel, which extends all the way down the plant.
3. Roots: Water molecules are pulled into the xylem from the cortex cells in the root, which pull water molecules from the root hair cells, which pull from the soil.
4. water is held in the leaf through adhesion (between water and other things)

Question 31

Factors influencing transpiration

Answer 31

1. Temperature
2. Humidity increase
3. Wind increase
4. Day and Night

Question 32

Temperature - transpiration

Answer 32

1. when temperature increases, transpiration increases because water is evaporating
2. The increased temperature causes more stomata to open
3. The increased temperature increases transpiration pull
4. It increases until there is another limiting factor that inhibits transpiration

Question 33

Humidity - transpiration

Answer 33

humidity increase decreases transpiration as the outside surroundings have higher concentration so there is a decreased natural desire to move (osmosis - high to low)

Question 34

Wind - transpiration

Answer 34

increasing wind increases transpiration as you are blowing the water vapour away so more water will move out

Question 35

day and night - transpiration

Answer 35

Plants lose more water during the day than they do at night.

Question 36

Transpiration stream

Answer 36

movement of water from the roots up through the xylem vessels to the mesophyll cells and then through the stomata

Question 37

Water potential gradient

Answer 37

1. water moves down a water potential gradient from high to low
2. highest water potential is in the soil and lowest is in the air
3. low water potential in leaves is caused by the loss of water vapour by transpiration

Question 38

Adaptations of a plant to help move up water

Answer 38

1. root hair cell has a large surface area so water can be absorbed efficiently
2. xylem vessels are hollow and narrow so that water has an easy pathway to flow up to the top of the plant
3. many air spaces inside the leaf mean that there is a large surface are of wet cell from which water can evaporate into the air which increases the rate of evaporation, thus speeding up the rate that water moves out of the xylem
4. stomata when open, allows water vapour to diffuse easily out of the leaf, which reduces water potential encouraging more water to evaporate from the surface of the mesophyll cells

Question 39

Measuring the rate of transpiration

Answer 39

1. potometers are used to measure the rate of transpiration
2. As water is lost through the plants leaves, the air bubbles moves
3. the speed of the bubbles movement shows the rate of water uptake
4. the is only an estimation as a small amount of the water taken up by the shoot is used in the leaves