9.1&9.2

Question 1

what is the function of a waxy cuticle

Answer 1

waterproof surface that prevents water loss

Question 2

what is the function of the upper epidermis?

Answer 2

protects the upper surface of a leaf but allows light through

Question 3

what is the function of the lower epidermis?

Answer 3

protects the under side of a lead

Question 4

what is the function of spongy mesophyll cells

Answer 4

photosynthetic tissue with large air spaces to allow for gas exchange

Question 5

what is the function of palisade mesophyll cells

Answer 5

tightly packed cells with many chloroplasts for photosynthesis

Question 6

what is the function of the xylem

Answer 6

specialised vessels that transport water

Question 7

what is the function of phloem

Answer 7

tubes that allow transport of organic solutes

Question 8

what is the function of the cambium

Answer 8

cells divide into new xylem and phloem

Question 9

what are vascular bundles

Answer 9

xylem, phloem and cambium

Question 10

what is the function of guard cells

Answer 10

specialised cells that open and close the stomata

Question 11

what is the function of a stomata pore

Answer 11

allows gas exchange

Question 12

How are carbon dioxide absorbed and oxygen released from a leaf?

Answer 12

CO2 diffuses into a leaf and O2 diffuses out of a leaf through the stomata

they both go down their concentration gradients

Question 13

What’s the problem for plants when stomata are open

Answer 13

layer of water in the cellulose cell walls of spongy mesophyll cells

this water is needed to dissolve CO2 into a solution

however, the water evaporates into the spongy mesophyll air spaces and diffuses out of the leaf by stomata

Question 14

Define Transpiration

Answer 14

the loss of water vapour from leaves

consequence of having stomata open during the day

Question 15

How do guard cells regulate the opening and closing of stomata

Answer 15

cells absorb water by osmosis and become turgid & expand which opens the stomata because one cell wall side is thicker than the other (kidney bean shape)

It closes once the water has been lost and the cells become flaccid

Question 16

explain the transpiration stream

Answer 16

water is lost by evaporation and diffuses out of the leaf through the stomata- which creates negative pressure

water is drawn out xylem vessels by adhesion the cellulose cell walls in mesophyll cells

This creates a pulling force in the xylem in the stem but does not collapse due to lignin rings

Cohesion transmits this pulling force from one molecule to the next all the way down the water column

Adhesion also helps water to be drawn up xylem vessel by capillary action

Water enters root hair cells by osmosis, is then pulled across the cortex and enters the xylem vessels in the root

Question 17

draw the structure of primary xylem vessels

Answer 17

XX

Question 18

Identification of root and stem tissues in microscope images

Answer 18

XX

Question 19

Explain how active uptake of mineral ions in the roots causes absorption of water by osmosis

Answer 19

active uptake of mineral ions causes a high concentration of solutes in the cytoplasm of root hair cells

water is passively absorbed by osmosis from an area of low solute concentration (soil) to high solute concentration (root hair cells cytoplasm) through a semi permeable membrane

Can be done by two routes; apoplast & symplast

apoplast:
- the movement of water through freely permeable cellulose cell walls & extracellular spaces by mass flow
- aided by adhesion to cellulose fibres
- main route for water across cortex

symplast:

• the movement of water through cell cytoplasm, b/w via plasmodesmata by diffusion
• to enter this route, water has to move across cell membrane by osmosis

Question 20

What are xerophytes ans halophytes

Answer 20

xerophytes- plants that live in dry conditions

halophytes- plants that live in salty conditions

Question 21

Name some adaptations to reduce water loss

Answer 21

fewer leaves or spires- reduces surface area over which water can be lost to transpiration

fewer stomata- reduces number of pores through which water can escape by transpiration

deep roots- can absorb water deep underground

shallow spreading roots- can cover large surface area to collect water rapidly during occasional rain

water storage structures- swollen leaves or stems can store water to be used during dry periods

Question 22

Explain how active transport is used to load organic solutes into phloem sieve tube at the source

Answer 22

organic solutes are loaded up into phloem sieve tube cells by a co-transporter mechanism

first, H+ ions are actively transported out of companion cells using ATP

This creates a high concentration of H+ ions outside of the cell

The H+ ions then flow down their concentration gradient into sieve tube cells through a co-transporter protein

The energy from this is used to carry sucrose into phloem sieve tube cells

This creates an increase of sucrose concentration in sieve tube cells at the source

Question 23

What is the consequence of high solute concentration in sources

Answer 23

High solute concentration in sieve tube cells decreases water concentration

water flows down its concentration gradient to enter sieve tube cells by osmosis

this generates high hydrostatic pressure in sieve tube cells at sources

Question 24

What is the consequence of low solute concentration in sinks

Answer 24

solutes leave the sieve tube cells

water concentration increases, so it leaves the sieve tube cells by osmosis and enters the xylem

this generate low hydrostatic pressure in sieve tube cells at sinks

Question 25

How are aphids used in measuring phloem transport rate

Answer 25

a branch is set up so that the leaves can photosynthesise in a glass chamber containing 14CO2

aphid colonies are allowed to feed on the phloem in the stem from 2 measured areas

the stylets are then severed (sap continues to flow = hydrostatic pressure) and is collected every 15 mins

the sap composition is analysed for presence of 14C so the flow rate b/w the two areas can be calculated

Question 26

What is the relationship between phloem sieve tube cells structure and function

Answer 26

they are living cells

they have no nucleus and few organelles (no resistance to flow of solutes)

they have pores in their need cell walls to allow solutes to pass easily

they have protein strands in their cytoplasm which connects to adjacent sieve tubes

they have companion cells that have a nucleus and organelles; controls the sieve tubes activity, produces proteins and ATP