Transport system in Plants

Question 1

Cell membrane

Answer 1

Exchange of substances such as: food molecules and waste products, occurs in the cell membrane

Question 2

What is Diffusion

Answer 2

Net movement of molecules from an area of high concentration to a low concentration down the concentration gradient

Question 3

What is Osmosis?

Answer 3

Movement of water molecules from a region of high water potential to low water potential through a semi-permeable membrane

Question 4

What is Active transport?

Answer 4

Movement of molecules from a region of low concentration to a high concentration against the concentration gradient

Question 5

What is the Uni-cellular and multicellular organisms SA?

Answer 5

Uni-cellular have a large surface area

Multi-cellular have a smaller surface area

Question 6

Function of the Xylem

Answer 6

Transport water and minerals from the roots to the stem and leaves
(xylem is always on the inside)

Question 7

Structural features of the Xylem

Answer 7

It is composed of dead cells which form hollow tubes.

Xylem cells are strengthened by lignin and so are adapted for the transport of water in the transpiration stream.

Question 8

Function of the Phloem

Answer 8

transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesizing leaves to non-photosynthesizing regions in the roots and stem.
This means that movement can be in any direction around the plant.
(phloem is always on the outside)

Question 9

Structural features of the Phloem

Answer 9

The cells are living cells and are not hollow.

Substances move from cell to cell through pores in the end walls of each cell.

Question 10

Root hair cells

Answer 10

They are adapted for the efficient uptake of water (by osmosis) and mineral ions (by active transport)

Question 11

Structure and function of Root hair cells

Answer 11

Root hairs are single-celled extensions of epidermis cells in the root
They grow between soil particles and absorb water and minerals from the soil
Root hairs increase the surface area to volume ratio significantly
This increases the rate of the absorption of mineral ions by active transport

Question 12

The route of water through the plant

Answer 12

Water moves, by osmosis, into the root hair cells, through the root cortex and into the xylem vessels:
Once the water gets into the xylem, it is carried up to the leaves where it enters mesophyll cells.
root hair cell → root cortex cells → xylem → leaf mesophyll cells

Question 13

What is Transpiration?

Answer 13

The loss of water vapour from the parts of the plant that are above ground (leaves, stem, flowers)

Question 14

How does transpiration occur?

process

Answer 14

• -> Loss of water occurs through evaporation of water at the surfaces of the spongy mesophyll cells followed by diffusion of water vapour through the stomata
• -> The many interconnecting air spaces between the mesophyll cells and the stomata creates a large surface area
• -> This means evaporation can happen rapidly when the stomata are open

Question 15

What is the effect of transpiration?

Answer 15

• -> Water moves through the xylem vessels in a continuous transpiration stream from the roots to the leaves via the stem to replace the water that has been lost due to transpiration
• -> Due to cohesion, the water in the xylem creates a continuous unbroken column (each individual molecule ‘pulls’ on the one below it)
• -> Transpiration produces tension or ‘pulls’ on the water in the xylem vessels
• ->If the rate of transpiration from the leaves increases, water molecules are pulled up the xylem vessels quicker

Question 16

What are the functions of transpiration?

Answer 16

• Transporting mineral ions
• Providing water to keep cells turgid in order to support the structure of the plant
• Providing water to leaf cells for photosynthesis
• Keeping the leaves cool, the conversion of water (liquid) into water vapour (gas) as it leaves the cells and enters the airspace requires heat energy. The use of heat to convert water into water vapour helps to cool the plant down

Question 17

What are the factors that affect transpiration?

Answer 17

Air movement
Humidity
Temperature
Light intensity

Question 18

Air movement

Answer 18

Air movement increases the rate of transpiration since the airflow removes the water vapor from the surrounding of the leaf which sets a concentration gradient between the air and the leaf, this increases water loss.

Question 19

Humidity

Answer 19

When the air is saturated with water vapor (humid) the concentration gradient is weaker so less water is lost.

Question 20

Temperature

Answer 20

At higher temperatures, particles have more kinetic energy so transpiration occurs faster as water molecules evaporate from the mesophyll and diffuse away faster.

Question 21

Light intensity

Answer 21

When the light intensity is high, the guard cells become turgid, since it is responsive to light, and then the stomata opens allowing water to be lost.

Question 22

What is used to investigate the effect of different conditions on the rate of transpiration?

Answer 22

Potometer

Question 23

What is a mass potometer?

Answer 23

measures a change in mass of a plant as a measure of the amount of water that has evaporated from the leaves and stem

Question 24

What is bubble potometer?

Answer 24

measures the uptake of water by a stem as a measure of the amount of water that is being lost by evaporation consequently pulling water up through the stem to replace it

Question 25

Rate of transpiration formula

Answer 25

Rate of transpiration = Distance moved by air bubble (m) / Time (min)