Topic 6 - Plants

Question 1

What is photosynthesis

Answer 1

When plants and algae trap energy (transferred by sunlight) and produce glucose

Question 2

Photosynthesis equation

Answer 2

carbon dioxide + water -> glucose + oxygen

6CO2 + 6H2O -> C6H12O6 + 6O2

Question 3

Where does photosynthesis occur

Answer 3

Chloroplasts containing chlorophyll (green pigment which traps energy transferred by light)

Question 4

What type of reaction is photosynthesis

Answer 4

Endothermic - products have more energy than reactants as it takes energy from surroundings

Question 5

What are factors affecting photosynthesis

Answer 5

1. Temperature
2. Carbon dioxide concentration
3. Light intensity
4. Distance from light

Question 6

How does temperature affect photosynthesis

Answer 6

Increase in temp = increase in rate

Reactions in photosynthesis are catlaysed by enzymes which work better in warmer temps

Question 7

How does carbon dixoide concentration affect photosynthesis

Answer 7

More CO2 = faster rate
It is a reactant for photosynthesis so reaction can occur faster

Question 8

How does light intensity affect photosynthesis

Answer 8

More light = more rate (DIRECTLY PROPORTIONAL)

Light provides more energy for reaction

Question 9

What is a limiting factor

Answer 9

A factor which at low levels prevents the rate of photosynthesis increasing

Question 10

How does distance from light source affect photosynthesis

Answer 10

INVERSELY PROPORTIONAL - further the distance, less photosynthesis

Question 11

How to find light intensity from distance

If lamp 2m away, intensity is?

Answer 11

Light intensity = 1/distance^2

intensity = 1/4

Question 12

Finding new light intensity when distance changes

Answer 12

Lnew = Loriginal x Distance^2original / D^2 new

Question 13

Root hair cell function

Answer 13

Absorbs water by osmosis and absorbs mineral ions by active transport. Found in tips of roots

Question 14

Root hair cell adaptations

Answer 14

1. ‘Hairs’ provide large surface area so water and mineral ions can be quickly absorbed
2. ‘Hairs’ have thin walls so short diffusion distance and flow of water into cells isnt slowed down.
3. Large vacuole so speed of osmosis is faster
4. Lots of mitochondria to provide energy for active transport

Question 15

Xylem function

Answer 15

For uptake of water anad mineral ions from roots to shoots

Question 16

Xylem adaptations

Answer 16

1. Cells are dead and their top and bottom cell walls disintegrate creating long empty vessels so water can move easily
2. Xylem vessles are rigid (thick walls and cells are lignified) so water pressure doesn’t burst vessels
3. Unidirectional (allows H2O to only travel up)

Question 17

Phloem function

Answer 17

Carries products of photosynthesis (incl sucrose) to all parts of plants

Question 18

Phloem adaptations

Answer 18

1. Sieve cells have holes which sucrose solution can flow through to be translocated
2. Companion cells have lots of mitochondria and cytoplasm (phloem doesn’t) to have lots of energy to pump sucrose in or out sieve cells
3. Small pores between it and sieve cells (to pump sucrose)
4. Bidirectional (sucrose travels up to growing shoots or down to storage organs)

Question 19

How does transpiration work?

Answer 19

1. Plant opens stomata to let in carbon dioxide, water on spongy mesophyll and palisade mesophyll evaporates and diffuses out of the leaf to atmosphere.
2. Water is drawn from xylem to replace lost water from leaves
3. Water molecules inside the xylem cells are strongly attracted to other water molecules. There is strong cohesion between the molecules because of hydrogen bonding. So, a continuous column of water is pulled up the stem in the transpiration stream by evaporation from the leaves.
4. As water travels through the xylem in the stem and leaf, it is being replaced by water taken up by the roots by osmosis.

Question 20

Transpiration function

Answer 20

1. provides water for photosynthesis
2. transports mineral ions
3. cools leaf as water evaporates
4. Provides water to keep cell turgid

Question 21

Adaptations of the guard cell

Answer 21

1. It opens and closes the stomata
2. Found in lower epidermis because lower surface is shaded and cooler so less water lost by transpiratiion
3. Open during day so diffusion of co2 and o2 can occur
4. Open when lots of water near (osmosis; h20 moves into guard cells so swells and opens)
5. closes at night so photosynthesis cant cocur (reduces transpiration + water is conserved)
6. closes when hot/losing water (becomes flaccid to reduce water loss)
7. Thin outer wals for gas exchange

Question 22

Factors affecting transpiration

Answer 22

1. Temperature
2. Humidity
3. Wind
4. Light intensity

Question 23

How does temperature affect transpiration?

Answer 23

Increase in temp = increase in rate

Increases evaporation of water out of leaves

Question 24

How does humidity affect transpiration?

Answer 24

Decrease in humidity = increase in rate

Humidity creates low water concentration in environment
If less humidity, larger concentration gradient between inside + outside of stomata so water diffuses quicker

Question 25

How does wind affect transpiration?

Answer 25

More wind = increase in rate wind moves water molecules away from stomata so larger concentration gradient

Question 26

how does light intensity affect transpiration?

Answer 26

More light = increase in rate More photosynthesis makes stomata open so H2O can diffuse out of the leaf

Question 27

How does translocation work

Answer 27

It is movement of sucrose from source to sink via phloem. Movement is bidirectional and an active process. 1. Sucrose is actively pumped into companion cells by active transport from source 2. Sucrose moves down the concentration gradient by diffusion from companion cells into the sieve tube 3. Sucrose moves out of sieve tubes by diffusion 4. it travesl through pores (plasmodesmata) of sieve tubes to sinks

Question 28

What does source to sink mean

Answer 28

Source (leaf) is place where photosythensis first occurs to produce sucrose from glucose Sink is where sucrose is stored as starch

Question 29

How is leaf adapted

Answer 29

1. Large surface area so lots of light absorbed 2. thin so short diffusion distance for co2 to travel to palisade mesophyll quickly (where photosynthesis occurs) 3. lots of chlorooplast contaning chlorophyll which traps light energy used for photosynthesis producing glucose 4. Chloroplasts move towards or away from light (protection from bright light damage) 5. Spongy mesophyll 6. Epidermis cells 7. Waxy cuticle 8. Veins 9. guard cells

Question 30

How is spongy mesophyll adapted

Answer 30

They are irregularly shaped which creates air spaces so gases can diffuse easily inside leaf.

Question 31

How is epidermis adapted

Answer 31

Lower and upper epidermis are transparent so light can enter easily

Question 32

How is waxy cuticle adapted

Answer 32

Produced by epidermis cells. Layer that is waterproof which prevents water loss

Question 33

How are veins adapted

Answer 33

Support leaf and transport water, mineral ions, sucrose

Question 34

How are leaves adapted for extreme weather conditions

Answer 34

- In winter, deciduous plants lose leaves preventing water loss. - Conifers have needle shaped leaves with small SA + think cuticle creating less wind resistance (can survive winds) - Water vapour is trapped close to leaves reducing water loss as diffusion is decreased

Question 35

What is stimulus

Answer 35

Change in the environment that causes a response by an organism

Question 36

What is a tropism

Answer 36

Response to stimulus by growing towards/away from it

Question 37

How does phototropism work in plants

Answer 37

- phototropism is tropism caused by light - plants SHOOTS are positively phototropic (towards light) so it gets more light for photosynthesis - plant ROOTS are negatively phototropic - It is caused by auxins - Auxins are produced in tips of shoots, if light is shone in one directioin, auxins move to shaded side, making cells on shaded side elongate, causing shoots to grow towards light

Question 38

What is gravitropism

Answer 38

Tropism caused by gravity

Question 39

how do plant shoots show gravitropism

Answer 39

Plant shoots show negative gravitropism (grow away from gravity). If shoots are horizontal, auxins move to lower side. Cells of shoot grow more on side with more auxins. So cell growth and cell elongation is stimulated on lower side, making shoot bend and grow upwards. Beneficial because more light is further away from the ground

Question 40

how do plant roots show gravitropism

Answer 40

Plant roots show positive gravitropism (grow towards gravity). If root is horizontal, auxin moves to the lower side. Cells of roots grow on side with less auxin so inhibits cell elongation and stimulates cells to grow on upper side, making root bends and grow down. Beneficial because more water and nutrients are lower down, and provides stability for plant.

Question 41

How are auxins used in commerical uses

Answer 41

1. As weed killers as artificial auxins are synthesised to only affect weeds. Increased auxin makes plant grow uncontrollably and die. 2. As rooting powders. Auxins cause plant cuttings to develop roots fast. Many identical plants can be produced fast.

Question 42

How are giberellings used in commercial uses

Answer 42

1. Allows seed germination by breaking seed dormancy so fruits can grow larger and flowering plants flower faster. 2. Giberelling cause plants to produce plants without being pollinated. Pollination causes seeds, so seedless fruits can be produced.

Question 43

How is ethene used in commercial uses

Answer 43

used to ripen fruits that were picked unriped as it stimulates enzymes that ripen fruit. Reduces wastage.