Plants

Question 1

What is the function and structure of the pits

Answer 1

These are areas where the cell wall is so thin, they are arranged in pairs with adjacent cells. To allow easy transport of substances

Question 2

What is the function and structure of the plasmodesmata

Answer 2

They are narrow fluid filled channels in the the cell walls, making the cytoplasm of one cell continuous with the cytoplasm of the next. This allows substances to be transported through and for communication. Often located in the pits, aiding the movement of substances between cells.

Question 3

Describe the structure of the xylem vessels

Answer 3

-Xylem tissue is found in the vascular bundle in the stem
-The xylem vessels are a long tube formed from dead cells
-The tubes are found together in bundles
-They have a hollow lumen and no end walls, which makes uninterrupted tubes, allowing water and mineral ions to pass up through the middle easily
-The walls are thickened with the woody substance lignin, which waterproofs it and provides support for the plant
-They contain pits which water and mineral ions move into and out of

Question 4

Describe the function of the xylem vessels

Answer 4

-The function is to transport water and mineral ions up the plant
-Another function is to provide the plant support

Question 5

Describe the structure of the phloem tissue

Answer 5

-The phloem tissue contains different types of cells including sieve tube elements and companion cells
-Sieve tube elements are living, and are joined end to end to from sieve tubes
-The ‘sieve’ parts are the end walls which are perforated, so have lots of holes in them to allow solutes to pass through
-However the sieve tubes have no nucleus, a very thin layer of cytoplasm and a few organelles. The cytoplasm of adjacent cells are connected through the holes in the plates
-The lack of nucleus and there organelles means the side tube elements can’t survive on their own. So there’s companion cell for every sieve tube element
-Companion cells carry out the living function for both themselves. For example providing the energy for the active transport of solutes

Question 6

Describe the function of the phloem tissue

Answer 6

The function of the phloem tissue is to transport organic solutes from where they are made to where they’re needed. This is known as translocation

Question 7

Describe the structure and function of the sclerenchyma fibres

Answer 7

The function of the sclerenchyma fibres is to provide support - they are not involved in transport
-The are made of bundles of dead cells that run vertically up the stem
-They have a hollow lumen, but unlike xylem vessels they DO have end walls
-There cells are also thickened with lignin
-They do not contain pits
-They contain more cellulose than other plant cells

Question 8

Where are xylem and phloem found

Answer 8

The xylem vessels, phloem tissue and sclerenchyma fibres are found through the plant in vascular bundles

Question 9

Compare the xylem and phloem

Answer 9

Xylem:
-One way flow
-Transport water and mineral ions
-No end walls
-Walls thickens with lignin
-Dead

Phloem
-Two way flow
-Transports organic substances
-Perforated End walls(Cell with holes in it)
-Walls have no lignin
-Alive

Question 10

State the sieve tube structure and function

Answer 10

Sieve plates with pores - Allow for the continuous movement of the organic compounds
Cellulose cell wall - Strengthens the wall to withstand the hydrostatic pressure that move the assimilates
No nucleus/vacuole/ribosomes - Maximises the

Question 11

State the companion cells structure and function

Answer 11

Nucleus and other organelles - Provide metabolic support to sieve tube elements and helps with loading and unloading of the assimilates
Transport proteins in plasma membrane - Moves assimilates into and out of the the sieve tube elements
Large number of mitochondria - To provide ATP for the active transport of assimilates
Plasmodesmata(Channels in the cell wall) - The link to sieve tube elements which allows organic compounds to move from the companion cells into sieve tube elements

Question 12

What is cohesion

Answer 12

The intermolecular forces between the water molecules

Question 13

What is adhesion

Answer 13

The intermolecular forces between water molecules and lignin

Question 14

How does water get transported in plants

Answer 14

-Water constantly evaporates from the surface of the cells of the leaves and diffuses through the stomata
-The water lost is replaced by water moving across the leaf from cell to cell
-This is turn draws water out of the xylem vessels due to tension
-Because there is cohesion which is the hydrogen boding between water molecules and adhesion which is the hydrogen bonding between the water molecules and lignin of the cell walls
-It causes columns of water to be continuously pulled up the xylem by the transpiration stream, aswell as help to offset the pull downwards due to gravity
-So water is constantly being removed from the roots into the xylem by diffusion, and water moves into the roots by active transport

Question 15

What is transpiration

Answer 15

-Transpiration is the loss of water from a plant surface by evaporation
-The water evaporates from the mist cell walls and accumulates in the spaces between cells in the leafs
-When the stomata open, it moves out of the leaf down a concentration gradient( Because there is more water inside the leaf than in the air outside)

Question 16

What are the four main factor affecting the transpiration rate

Answer 16

-Light - the lighter it is the faster the rate of transpiration, because the stomata open when it gets light to let in co2 for photosynthesis. When it is dark the stomata are usually closed, as there is little transpiration.
-Temperature - The higher the temperature the faster the transpiration rate. Because warmer water have more energy so they evaporate from the cells inside the leaf faster. This increases the concentration gradient between the inside and the out side of the leaf, making water diffuse out of the leaf faster
-Humidity - the lower the humidity, the faster the transpiration rate, because if the air around the plant is dry, the concentration gradient between leaf and the air is increased, which increase transpiration.
-Wind - the windier it is, the faster the transpiration rate, Lots of air movement blows away the water molecules from a round the stomata, this increase the water potential gradient between the inside of the leaf and the outside. Therefore increase the concentration gradient, which increases the rate of transpiration.

Question 17

What is translocation

Answer 17

Translocation is the movement of solutes to where theyre needed in a plant. Solutes are sometimes called assimilates
-Its an energy-requiring process
-Translocation moves solutes from ‘sources’ to ‘sinks’
-The source of a solute is where it’s made(so it has a high concentration)
-The sink is the area where it’s used up(so its at a lower concentration there)
-Enzymes maintain a concretion gradient from the sources to the sink by changing the solutes at the sink(by breaking them down or making them into something else). This makes sure there’s always a lower concentration at the sink than at the source

Question 18

Explain the Mass Flow Hypothesis

Answer 18

This is a representation of how solutes are transported from the source to sink by translocation
1) Active transport is used to actively load the solutes from companion cells into sieve tubes of the phloem at the source
2)This Lowers the water potential inside the sieve tubes, so water enters the tubes by osmosis from the xylem and companion cells
3)This cares a high pressure inside the isles tubes at the source of the phloem
4)At the sink end, solutes are removes from the phloem to be used up
5)This increases the water potential inside the sieve tubes, so water also leaves the tube by osmosis
6)This lowers the pressure inside the sieve tubes
7)The result is a pressure gradient from the source end to the sink end
8)This gradient pushes solutes along the side tubes towards the sink
9) When they reach the sink the solutes will be used(e.g. in respiration) or stored(e.g. as starch)

Question 19

Explain the movement of solutes through the phloem

Answer 19

-Organic substances/sugar produced in leaf
-Pumped into phloem sieve tubes through diffusion and active transport with the help of mitochondria in the companion cells
-High concentration of sucrose in sieve tube/phloem at the leaf end
-Water into phloem by osmosis and raises pressure at the leaf end
-Water moves to sink
-Sink uses up organic molecules quickly/low concentration
-Sucrose moves into the sink by facilitated diffusion and active transport
-Reduced pressure in the phloem cause the water to move back into the xylem

Question 20

Describe the autolysis

Answer 20

-First the plant produces a plolymer called lignin. Which impregnates the cellulose cell wall and, as the cells become lignified, the entry of water and solutes into them is restricted.
-At the same time, the tonoplast breaks down, and there is autolysis of the cells contents
-During autolysis, the cell organelles , cytoplasm and cells membrane are broken down by the action of enzymes and are lost. Leaving dead empty cells that form tubes

Question 21

How does the structure of the sclerenchyma fibres make them useful for rope

Answer 21

-They have thick lignified walls which provide strength, therefore will not break easily
-Using lignin will make the rope waterproof
-Are light due to hollow lumen

Question 22

Canola is a plant grown as a crop because the seeds are rich in oil. The extracted oil is used in cooking and as a sustainable fuel. Suggest why the production of oil from Canola seeds can be described as sustainable.(2)

Answer 22

-Because canola can be grown
-It is renewable
-And the resource can be made available for future generations

Question 23

Explain the relationship between the structure and functions of a granum in photosynthesis.

Answer 23

-Granum is formed from many layers of thylakoid membrane to increase surface area(for absorbing light)
-Thylakoid membranes contain chlorophyl to to absorb light
-Electron carrier molecules in thylakoid in membrane involved in atp production

Question 24

Explain the role of the middle lamella when a plant cell completes mitosis.

Answer 24

-Its produced between adjacent new cells
-Because the middle lamella holds the cell walls together

Question 25

Explain the structure and function of the plasmodesmata