Chapter 8

Question 1

State the functions of xylem and phloem

Answer 1

1. xylem transports minerals ions and water from the root hair cells into the leaves by transpiration
2. phloem transports sucrose and amino acids from the leaves to the other parts of the plant by translocation

Question 2

describe the xylem

Answer 2

1. thick walls made out of lignin - very strong to help keep plant upright - and cellulose
2. No cell contents - no cytoplasm or nuclei
3. dead cells join end-to-end with no cross walls to form a long continuous tube

Question 3

how are root hair cells adapted for water uptake

Answer 3

Root hair cells are adapted to have a greatly increased surface area, optimising for a great ability to intake water and ions.

Question 4

describe how water enters the cell

Answer 4

1. Water enters by osmosis
2. Water passes across the root from cell-to-cell, by osmosis. it also seeps between cells
3. water is drawn up the xylem vessels as transpiration is constantly removing water from the top of them

Question 5

what is transpiration? How does it happen?

Answer 5

it is the loss of water vapour from leaves by when water evaporates from the surface of the mesophyll cells into the air spaces and then diffuses out of the leaves through the stomata as water vapour

Question 6

explain the connection between the leaf’s structure and how water is lost as water vapour

Answer 6

The many air spaces inside the leaf let water evaporate from mesophyll cells, creating more water vapour that can diffuse out through the leaf.

Question 7

How do the size and number of stomata affect water vapour loss?

Answer 7

The more stomata a leaf has, and the bigger they are, the faster water vapour can escape.

Question 8

How does water move upwards in the xylem?

Answer 8

Transpiration causes water to evaporate from leaves, creating a suction in the xylem.

Question 9

What keeps the water column unbroken in the xylem?

Answer 9

Water molecules stick together by cohesion (hydrogen bonding), allowing them to be pulled upward as one continuous column during transpiration.

Question 10

How does temperature affect the rate of transpiration?

Answer 10

Higher temperature increases evaporation and diffusion rates, so transpiration increases. Lower temperature reduces both, slowing transpiration.

Question 11

How does wind speed affect transpiration?

Answer 11

Stronger wind increases transpiration by removing humid air around stomata, while calm air slows transpiration by allowing humidity to build up.

Question 12

How does humidity affect transpiration?

Answer 12

High humidity reduces the concentration gradient between leaf and air, lowering transpiration.
Low humidity increases the gradient, raising transpiration.

Question 13

What is flaccid and how does it occur?

Answer 13

Flaccid cells have lost water and become soft. This happens when the plant loses water faster than the roots can replace it, causing leaves to droop and stomata to close.

Question 14

Why does wilting reduce further water loss?

Answer 14

Closed stomata limit evaporation, and drooping leaves reduce surface area exposed to sunlight and air, decreasing transpiration.

Question 15

describe how the loss of water vapour occurs in cells

Answer 15

1. water moves from the xylem vessels to the mesophyll cells by osmosis
2. water evaporates from the surface of the mesophyll cell walls
3. the air spaces contain water vapour
4. water vapour diffuses out the air spaces, through the stomata

Question 16

How does water vapour loss from leaves help pull water upward through the plant?

Answer 16

As water vapour leaves the leaf, suction occurs, pulling water and dissolved ions upward through the xylem. This process is aided by the large internal surface area of mesophyll air spaces and the size and number of stomata, which increase water vapour loss.

Question 17

describe what is meant by flaccid and turgid

Answer 17

Flaccid means when a plant is wilting. turgid means when the plant healthy

Question 18

why can plants become flaccid?

Answer 18

Wilting occurs when a plant loses water faster than its roots can absorb it, causing cells to lose turgor pressure and become soft.

Question 19

What is translocation, and how do sources and sinks relate to it?

Answer 19

Translocation is the transport of sucrose and amino acids in the phloem from sources (producing or releasing areas) to sinks (using or storing areas). A plant part can switch roles depending on its needs or growth stage.

Question 20

Explain what a source and sink is

Answer 20

1. Source: Part of a plant that releases sucrose or amino acids, to be transported to other parts
2. Sink: part of a plant to which sucrose or amino acids are being transported, and where they are used or stored

Question 21

In translocation, which parts of the plant act as sources and which as sinks?

Answer 21

Leaves are sources, while parts like flowers and roots are sinks.

Question 22

How do flowers and roots use the sucrose they receive?

Answer 22

Flowers convert sucrose into fructose for nectar and fruits; roots change it into starch for storage.

Question 23

When does translocation mainly occur?

Answer 23

When the plant is photosynthesising and growing actively.

Question 24

What happens to a plant’s activity when the climate becomes harsh?

Answer 24

The plant becomes less active, often losing its leaves.

Question 25

How do the roles of sources and sinks change during harsh conditions?

Answer 25

Roots become sources, sending stored materials to leaves, which become sinks.

Question 26

How do the functions of the phloem and xylem differ?

Answer 26

Phloem transports materials both upward and downward; xylem only moves water upward by transpiration.

Question 27

describe the phloem

Answer 27

Located in vascular bundles alongside xylem, in leaves, stems, and roots. Supports growth, energy supply, and storage in different parts of the plant. contain cell content but have no support it is dead cells are connected by pores

Question 28

What is transpiration?

Answer 28

Transpiration is the evaporation of water from a plant’s leaves, mainly through the stomata. This loss of water creates a pull that draws more water up through the xylem from the roots to the leaves

Question 29

What is translocation?

Answer 29

Translocation is the movement of dissolved sugars (mainly sucrose) and other substances through the phloem of a plant. It transports food from the leaves (where it’s made in photosynthesis) to other parts of the plant for growth, storage, or respiration.