Plant Structures And Functions

Question 1

What is photosynthesis?

Answer 1

An endothermic reaction(takes in light from the sun) which occurs in the chloroplasts
-6carbon dioxide + 6water — (light)— glucose + 6oxygen

Question 2

How can we tests a lead to identify the presence of starch?

Answer 2

• boil the leaf in water to make it floppy do it can fit in the test tube
• place in ethanol to remove the chlorophyll to de colourised it
• add iodine and where starch is present the will turn blue/black

Question 3

What is the law of limiting factors?

Answer 3

When a process depends on two or more factors, the rate if the process is limited by the factor which is in shortest supply

Question 4

How does carbon dioxide effect the rate of photosynthesis?

Answer 4

As carbon dioxide increases so does the rate of photosynthesis until it reaches a maximum rate. It increases because CO2 is a raw material needed in photosynthesis. The rate increase until another factor begins to limit it

Question 5

What effect does light have on the rate of photosynthesis?

Answer 5

Light transfers the energy needed for photosynthesis. As light level is raised, the rate if photosynthesis increases steadily but only up to a certain point until another factor starts to limit it.

Question 6

How does temperature effect the rate of photosynthesis?

Answer 6

As temperature increases, the rate increases until it reaches the optimum temperature and then it decreases again.
-temperature increases the rate of chemical reactions as particles have more Kenergy. When optimum temp passes the enzymes denature so the rate decreases

Question 7

What adaptations and processes do root hair cells partake in?

Answer 7

• root hair cells have hairs to provide a large surface area, many mitochondria and a thin cell wall
• minerals are absorbed by active transport into the cell as there is usually a higher concentration
• water is absorbed through diffusion as there is usually a higher concentration of water in the soil

Question 8

What is transpiration?

Answer 8

The loss of water from plants which tends to happen in the leaves

Question 9

What is the xylem?

Answer 9

Xylem tubes are made from dead cells joined together and strengthen by lignin so the walls don’t collapse. There are no end walls to impede water flow and has a hole down the middle
They carry water and mineral ions from the roots to the stem and leaves

Question 10

How does transpiration work?

Answer 10

• water passes into the lead by osmosis to replace the water which has been lost
• water containing mineral ions is pulled upwards through xylem vessels as they contain a continuous column of water due to weak forces of attraction between water molecules
• water evaporates from the stomata

Question 11

What is a potometer?

Answer 11

Can estimate the rate if transpiration but is only an estimate as it measures water uptake but some is used in photosynthesis

Question 12

What is a stomata?

Answer 12

Stomata only open if there is enough water in the guard cell and are used for gas exchange. When the stomata opens to let CO2 in and looses water through diffusion.
-most stomata are underneath the leaf to limit evaporation

Question 13

How does light effect the rate of transpiration?

Answer 13

In bright light transpiration increase as more light means more photosynthesis. This means the stomata opens more to allow CO2 in so more water is lost

Question 14

How does temperature effect the rate if transpiration?

Answer 14

Transpiration is faster in hotter temperatures as evaporation and diffusion take place at a faster rate as they have more energy. Warm air is also able to absorb more water vapour than cool air.

Question 15

How does humidity effect rate of transpiration?

Answer 15

Transpiration is slower in humid conditions as diffusion slows down as the air is already saturated with water molecules. This creates a lower concentration gradient

Question 16

How does wind effect the rate of transpiration?

Answer 16

Transpiration is faster in windy conditions as saturated air with water vapour is removed quickly by air creating drier are to speed up diffusion

Question 17

What is a positive outcome of transpiration?

Answer 17

It cools the plant as water evaporates

Question 18

How does a thicker waxy cuticle of a xerophyte reduce transpiration and help it survive?

Answer 18

Reduces water loss through epidermis as it is hydrophobic. This means less evaporation and so less transpiration

Question 19

How does small leaves/needles of a xerophyte reduce transpiration and help it survive?

Answer 19

Deciduous plants loose leaves during winter when they may not be able to photosynthesis. This means there is a smaller surface area and fewer stomata so there is less evaporation and transpiration

Question 20

How does sunken stomata (pits) of a xerophyte reduce transpiration and help it survive?

Answer 20

Stomata on the underside of the leaf to reduce direct heating and transpiration
-hairs trap water vapour which stops the wind removing it. Thus there is more water particles around the leaf(humid air)which reduces the concentration gradient and therefore transpiration

Question 21

How does a stomata shutting in the night and opening in the day of a xerophyte reduce transpiration and help it survive?

Answer 21

Stomata closes at night so there is no light for photosynthesis so no water is lost
It is also warmer in the day so there is more evaporation

Question 22

How are leaves adapted to benefit gas exchange in photosynthesis?

Answer 22

• leaves are broad so a large surface area is exposed to light
• the palisade layer has a lot of chloroplasts
• the epidermal tissues are covered with a waxy cuticle which helps reduce water loss by evaporation

Question 23

What is translocation and the role of phloem?

Answer 23

Plants make sucrose from the glucose which is made in photosynthesis-this is translocated in the phloem vessels and is transported to all parts of the plant

Question 24

What are the first 3 stages of translocation?

Answer 24

• starch is made by photosynthesis in chloroplasts
• starch is broken down when it is dark and the products of the breakdown are moved into the cytoplasm of the cell
• starch is used to make sucrose which is a Soluble sugar

Question 25

What are stages 4 and 5 and 6 of translocation?

Answer 25

- sucrose is moved by active transport into companion cells - companion cells pump sucrose into sieve cells - the sieve and companion cells form phloem. The pumping of sucrose into the sieve cells causes a pressure difference causing the content of the sieve cell to move up or down

Question 26

What are the adaptations of companion cells and sieve cells?

Answer 26

- Companion cells have many mitochondria to release energy and have small pores between them and sieve cells - sieve cells have no nucleus and only small cytoplasm in order to make the central channel wider to make the flow of liquids easier

Question 27

What is a tropism?

Answer 27

Responding to a stimulus by growing away or towards it (e.g. light, gravity and water)

Question 28

What are auxins?

Answer 28

Auxins are plant hormones which inhabit growth in the roots and stimulate growth in the shoots of plants - they are found in the meristem

Question 29

What is positive and negative tropism?

Answer 29

Positive tropism is going towards the stimulus | Negative tropism is going away from the stimulus

Question 30

What is the stimulus for the tropism needed to know?

Answer 30

- phototropism = sun - gravitropism = gravity - hydrotropism = water

Question 31

Are shoots positively or negatively gravitropic and why?

Answer 31

Shoots are negatively geotropic as when a shoot grown out sideways it produces an unequal distribution of auxin in the tip with more auxin on the lower side. -this cause the lower side to grow more bending the shoot upwards

Question 32

What shoots positively or negatively phototropic and why?

Answer 32

Shoots are positively phototropic -when a shoot is exposed to light it accumulates more auxins on the shady side than the side exposed to the light. This causes the lower side to elongate and grow faster, bending the shoot upwards

Question 33

Are roots positively or negatively gravitropic?

Answer 33

Positively gravitropic -roots growing sideways will always have more auxins on its lower side but in the root the extra auxins inhabits growth. This means the cell on top elongates faster and the root bends downwards

Question 34

Are roots positively or negatively phototropic?

Answer 34

Roots are negatively phototropic -if roots start being exposed to light more auxins accumulate on the lower, shaded side so the root bends downwards back into the ground.

Question 35

How are plant hormones used for selective weed killers?

Answer 35

- most weeds are broad leaves in contrast to grass etc which have very narrow leaves - selective weedkillers use auxins that only affect broad leaves plants - they totally disrupt their normal growth patterns which soon kills them but leaves the grass or other crops untouched

Question 36

How are plant hormones used for rooting powder?

Answer 36

- normally if you stick a cutting of a plant in the soil they won’t grow but if you add rooting power which contain auxins they will rapidly produce roots and grow a new plant. - this enable growth of clones of a good and rapid growing plants - quicker as don’t need to wait for growth from seeds and more plants produces from same number of seeds

Question 37

How are plant hormones used for producing seedless fruit?

Answer 37

- fruits with seeds normally only grow on flowering plants once pollinated - if plant hormones such as gibberellins are applied to un-pollinated flowers the fruit will grow but the seeds won’t . Can grow larger with greater biomass - they can slo control the time of heat when seeds germinate to ensure they all harvest at the same time

Question 38

How can plant hormones be used to control the ripening of fruits?

Answer 38

- can be controlled either while still on the plant or during transportation. - this allows the fruit to be unpicked while It’s still unripe (firmer and less easily damaged) - a ripening hormone called ethene is then added and the fruit will ripen on the way to the shop and then be better to eat.

Question 39

How does carbon dioxide enter the cell?

Answer 39

Through diffusion into the stomata from an area of high concentration to an area of low concentration

Question 40

What re some advantages of positive gravitropism and phototropism?

Answer 40

- PG can provide strong roots for stability and means they can reach more water and mineral ions in deeper areas of soil - PP means they can get more sunlight so more photosynthesis to provide glucose