4.2.3.2 Plant Organ System

Question 1

What is the function of a phloem?

Answer 1

• transport food substances (mainly dissolved sugars) made in leaves for immediate use or storage

Question 2

What is phloem made up of?

Answer 2

• columns of elongated living cells with small pores in the end walls to allow cell sap to flow through

Question 3

What direction do the food substances go in?

Answer 3

• both directions

Question 4

What is the process the phloem do?

Answer 4

• translocation

Question 5

What is the function of a xylem?

Answer 5

• transports water up
• carry mineral ions
• from root to stem and leave

Question 6

What is xylem made up of?

Answer 6

• dead cells joined end to end with no end walls between them and a hole down the middle
• strengthened with material called lignin

Question 7

What is the transpiration stream?

Answer 7

• movement of water from roots, through xylem and out of the leaves

Question 8

What is transpiration?

Answer 8

• loss of water from plant
• mostly in leaves

Question 9

What is transpiration caused by?

Answer 9

• evaporation and diffusion of water from a plant’s surface

Question 10

What does evaporation create?

Answer 10

• slight shortage of water in leaf
• so more water is drawn up from rest of plant through xylem vessels
• in turn means more water drawn from roots so there is a constant transpiration stream

Question 11

Why is transpiration just a side-effect of how leaves are adapted for photosynthesis?

Answer 11

• they have to have stomata so gases can be exchanged but there is more water inside than air outside so water escapes from leaves through diffusion

Question 12

What are the main factors that affect transpiration rate?

Answer 12

• light intensity
• temperature
• air flow
• humidity

Question 13

How does light intensity affect transpiration rate?

Answer 13

• the brighter the light, the greater the rate of transpiration
• stomata close when it’s dark because photosynthesis doesn’t happen in the dark, little water can escape

Question 14

How does temperature affect transpiration rate?

Answer 14

• the warmer it is, the faster transpiration happens
• water particles have more energy to evaporate and diffuse

Question 15

How does air flow affect transpiration rate?

Answer 15

• the better the air flow around a leaf, the greater the transpiration rate
• if poor, water vapour just surrounds the leaf and doesn’t get swept away, so there is a high concentration outside and inside the leaf so diffusion doesn’t happen fast

Question 16

How does humidity affect transpiration rate?

Answer 16

• the drier the air around a leaf, the father transpiration happens
• the same occurs when air flow is too much outside a leaf

Question 17

How do you estimate the rate of respiration?

Answer 17

• measuring an uptake of water by a plant
• you can assume a water uptake by plant is directly related to water loss
• set up a potometer and then start a stopwatch when an air bubble is visible
• record distance moved by bubble per unit time
• keep conditions constant throughout

Question 18

How are guard cells adapted to open and close stomata?

Answer 18

• kidney shape which opens and closes stomata
• when plant has lots of water, guard cells fill with it and go turgid which makes stomata open so gases can be exchanged
• when plant is short of water, guard cells lose water and become flaccid which make stomata close
• thin outer walls and thickened inner walls make it open and close
• sensitive to light and close at night to save water
• tend to find more on undersides as it’s shaded and cooler so less water loss

Question 19

What is a guard cells function?

Answer 19

• gas exchange
• controlling water loss within a leaf