biology chapter 8

Question 1

what is the vessel that are called transport or vascular tissues

Answer 1

Flowering plants have a system of vessels that run up and down the plants carrying materials

Question 2

what are the two types of vascular tissues in plants

Answer 2

xylem and phloem

Question 3

what are the functions of xylem

Answer 3

• conducting water and dissolved mineral ions from roots to the stems and the leaves
• providing mechanical support for the plant

Question 4

what are the functions of phloem

Answer 4

conducting manufactured food substances from the green parts of the plant especially the leaves to other parts of the plant

Question 5

how is a xylem vessel adapted for its function

Answer 5

the inner walls of xylem vessels are strengthened by the deposits of a substance called lignin

Question 6

how is the phloem adapted for its function

Answer 6

it consists of mainly of long tubes called sieve tubes and companion cells. Sieve tubes are made up of living cells

Question 7

what is the vascular bundle made of

Answer 7

xylem and phloem

Question 8

what is between the xylem and phloem inside the vascular bundle

Answer 8

cambium

Question 9

what is in the centre of the dicotyledonous stem

Answer 9

pith

Question 10

what wraps around the pith and the vascular bundle

Answer 10

cortex

Question 11

what wraps around the whole dicotyledonous stem

Answer 11

epidermis

Question 12

how can we study the path of water takes through a plant

Answer 12

• the xylem tissue has been stained in red
• xylem is the tissue involved in the uptake and transport of water

Question 13

why does the aphid feed on the phloem of the plant

Answer 13

The phloem transports sucrose and amino acids around the plant. Sucrose and amino acids provide food for the aphid. Amino acids allow the aphid to build up proteins

Question 13

how can we study the path food substances take through a plant

Answer 13

the transport of manufactured food substances such as sucrose and amino acids in plants is known as translocation

Question 14

using the ‘ringing’ experiment, how can we study the path food substances take through a plant

Answer 14

The transport of manufactured food substances from the leaves occurs through the phloem.

Manufactured food substances, such as sugars and amino acid, accumulate above the cut region and cause swelling.

Question 14

what is the source of translocation

Answer 14

Supplies food substances such as sucrose and amino acids to other parts of the plant. for example, leaves

Question 15

what is the sink of translocation

Answer 15

Stores food substances.Sometimes the source can become the sink
for example, the stem, roots

Question 16

how does the water enter a plant

Answer 16

absorption of water takes place through the root hairs. root hairs also absorb mineral ions from the soil solution

Question 17

how do root hairs absorb mineral ions

Answer 17

the root cell absorbs mineral ions from the soil solution by active transport. it uses energy from respiration to absorb the ions against a concentration gradient

Question 17

what is transpiration

Answer 17

transpiration is the loss of water vapour from the aerial parts of a plant, mainly through the stomata of the leaves

Question 17

how is the root hair cell adapted for its function of absorption

Answer 17

the root hair cell is long and narrow, which increases its surface area to volume ratio. this increases the rate of absorption of water and mineral ions

Question 18

what is cuticular transpiration

Answer 18

during transpiration, most of the water vapour is lost from the inside of the leaf, not from the leaf surfaces. this is because the cuticle covering the leaf surface is relatively impermeable to water. however, a very small amount of water may evaporate directly from the surfaces of the epidermal cells. this is cuticular transpiration

Question 19

how is transpiration involved in moving water against gravity

Answer 19

the evaporation of water from the leaves remove the water from the xylem vessels. this results in a suction force which pulls water up the xylem vessels. this suction force due to transpiration is known as transpiration pull. it is the main force in drawing water and mineral ions up the plant. the stream of water up the plant is called the transpiration stream.

Question 20

describe the water movement inside a leaf

Answer 20

• water continuously moves out of the mesophyll cells to form a thin film of moisture over their surfaces
• water evaporates from the thin film of moisture and moves into a large surface area of interconnecting intercellular air spaces. water vapour accumulates in the large air spaces near the stomata.
• water vapour diffuses through the stomata to the drier air outside the leaf. this is transpiration. an increase in the size and the leaf and number of stomata in the leaf increases the rate of traanspiration

Question 21

what is the importance of evaporation

Answer 21

Transpiration draws water and mineral ionsfrom the roots to the stem and leaves. Evaporation of water from the cells in the leaves removes latent heat of vaporisation.  Water transported to the leaves can be used in photosynthesis, to keep cells turgid, and to replace water lost by the cells.

Question 22

using a potometer

Answer 22

it is difficult to measure the rate of transpiration directly because some of the water taken in by the plant is used up in photosynthesis. however, the rate of water absorption can be measured directly. a potometer is used to directly measure the rate of water absorption by a plant

Question 23

what are the factors that affect the rate of transpiration

Answer 23

transpiration is affected by evaporation. therefore, any factor that affects the rate of evaporation of water will affect the rate of transpiration. these include, air movement, temperature, light and humidity and wiliting

Question 24

how does wind or air movement affect the rate of transpiration

Answer 24

wind blows away the water vapour that accumulates outside the stomata. this maintains the water vapour concentration gradient between the leaf and the atmosphere. thus the stronger the wind, the higher the rate of transpiration

Question 25

how does temperature of air affect the rate of transpiration

Answer 25

assuming that other factors remain constant, a rise in the temperature of the surroundings increases the rate of evaporation of water from the cell surfaces. thus, the rate of transpiration is higher at higher temperature

Question 26

how does light affect the rate of transpiration

Answer 26

light affects the size of the stomata on the leaf. it will therefore affect the rate of transpiration. under sunlight, the stomata opens and becomes wider. this increases the rate of transpiration. in the dark, the stomata closes so less water is lost from the leaf

Question 27

how does humidity of the air affect the rate of transpiration

Answer 27

the intercellular air spaces in the leaf are normally saturated with the water vapour. this is a water vapour concentration gradient between the leaf and the atmosphere. when the air outside the leaf is drier or less humid, the concentration of the water vapour is steeper

Question 28

what is the advantage of wilting

Answer 28

when the leaf folds up due to wilting, the surface area that is exposed to the sunlight is reduced. excessive loss of water causes the guard cells to become flaccid and the stomata to close. thus the rate of transpiration is reduced

Question 28

how does wilting affect the rate of transpiration

Answer 28

the turgor pressure in the mesophyll cells of the leaf helps to support the leaf and keep it firm. this enables it to spread out widely to absorb sunlight for photosynthesis. in strong sunlight, when the rate of transpiration exceeds the rate of absorption of water by the roots, the cells lose their turgor

Question 29

what is the disadvantage of wilting

Answer 29

the rate of photosynthesis is reduced because water becomes a limiting factor. as the stomata are closed, the amount of carbon dioxide entering the leaf is also reduced. carbon dioxide becomes a limiting factor and the rate of photosynthesis is decreased.