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Biology edexcel 9-1 > Topic 6 > Flashcards

Topic 6 Flashcards

1
Q

Give examples of photosynthetic organisms

A

green plants and algae

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2
Q

How are these photosynthetic organisms the main producers of food?

A
  1. They use energy from the sun to make glucose
  2. some of the glucose is used to make larger, complex molecules that plants/algae need to grow. (these makes up biomass)
  3. energy stored in biomass works its way through food chains as animals eat them and each other
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3
Q

What is biomass?

A

mass of living material

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4
Q

Is photosynthesis an endothermic or exothermic reaction?

A

An endothermic reaction (energy is taken in)

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5
Q

What is the symbol and word equation for photosynthesis?

A

Carbon dioxide + water (arrow with light and chlorophyll) glucose + oxygen

6CO2 + 6H20 (arrow with light above and chlorophyll below) C6H1206 + 602

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6
Q

What three things are limiting factors on the rate of photosynthesis?

A
  1. Temperature
  2. light intensity
  3. Conc of CO2
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7
Q

Describe how you could investigate the effect of light intensity on the rate of photosynthesis?

*PW = pondweed

A
  1. set up apparatus. gas syringe should be empty at start and sodium hydrogencarbonate could be added to provide plant with CO2
  2. place source of light at specific distance from PW
  3. allow PW to photosynthesis for set amount of time
  4. O2 released will collect in the syringe (volume)
  5. repeated with light source at different distances
  6. rate of oxygen produced - volume / time
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8
Q

What should we control during the core practical?

A
  • temperature (by putting flask into a water bath)

- and CO2 conc (adding set amount of sodium hydrogencarbonate to set amount of water)

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9
Q

Explain how light intensity affects the rate of photosynthesis?

A
  1. as light intensity increases, so does the rate. (to a certain point)
  2. After the point, either conc of co2 or temp will become the limiting factor
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10
Q

what is the inverse square law?

A

light intensity = 1/distance squared

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11
Q

How does carbon dioxide affect the rate of photosynthesis?

A

Increasing the conc of CO2 will increase the rate of photosynthesis up to a certain point

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12
Q

How does temperature affect the rate of photosynthesis?

A
  • Temp cant be too low as enzymes work slow at lower temperatures
  • Temp cant be too high (45 degrees) as to not denature the enzymes
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13
Q

How do root hair cells allow plants to absorb water and minerals?

A

They give the plant a large surface area for absorbing water (through osmosis) and minerals (through active transport as the conc of minerals is higher in the root hair cells than in the soil)

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14
Q

What are phloem tubes made out of?

A

Elongated living cells with small pores in the end walls to allow stuff to flow through

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15
Q

What is translocation?

A

A process in phloem tubes that transports sucrose made in the leaves to the rest of the plant for immediate use or for storage. The process requires energy from respiration and the transport goes in both directions

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16
Q

What are xylem tubes made out of?

A

They are made out of dead cells joined end to end with no end walls between them and a hole down the middle. Theyre strengthened with a material called lignin

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17
Q

What is the main function of xylem tubes?

A

They carry water and mineral ions from the roots to the stem and leaves

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18
Q

What is the transpiration stream?

A

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

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19
Q

Outline what transpiration is

A

The loss of water from a plant

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20
Q

Describe transpiration (process)

A

1, This is caused by evaporation and diffusion of water from plants surface( mostly happens at leaves)
2. This creates a shortage of water in leaf, and so more water is drawn up from rest of plant through xylem vessels to replace it
3 As more water is drawn up, theres a constant transpiration stream of water through plant
4. The transpiration stream also carries along mineral ions that are dissolved in the water along with it

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21
Q

What are stomata?

A

Tiny pores found on the lower surface of leaves

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22
Q

How do stomata relate to gases and transpiration?

A

They allow CO2 and oxygen to diffuse directly in and out of a leaf. They also allow water vapour to escape during transpiration as the conc of water vapour is higher inside the cell so water escapes through the stomata

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23
Q

What are guard cells?

A

These are cells that surround the stomata and change shape to control the size of the pore. When the guard cells are turgid (swollen with water), the stomata are open and when the guard cells are flaccid (low on water), the stomata are closed

24
Q

What three factors affect transpiration rate?

A
  1. Light intensity
  2. Temperature
  3. Air flow
25
Q

How does light intensity affect transpiration rate?

A

The brighter the light, the greater the transpiration rate as stomata are closed when its darker (they dont need to be open in the dark as photosynthesis only happens in the light so they can let CO2 in)

26
Q

How does temperature affect transpiration rate?

A

The warmer it is, the faster transpiration happens. When its warm, the water particles have more energy to evaporate and diffuse out of the stomata

27
Q

How does air flow affect transpiration rate?

A

The better the air flow around a leaf, the greater the transpiration rate. This is because e.g. poor air flow means that water particles will surround the leaf, meaning a high conc of water particles outside the lead than inside. If there is good air flow, water particles are swept away, maintaining a low conc of water in the air than outside the leaf. (this allows diffusion to happen)

28
Q

How can you estimate transpiration rate?

A

Using a potometer, measure the water uptake of a plant and use the equation. speed = distance / time. you can use a potometer to estimate how light intensity, temparature or air flow affect transpiration rate by only changing the variable and controlling the rest

29
Q

How are leaves adapted for photosynthesis?

A

They are broad, so that there is a large surface area exposed to light. This is needed for photosynthesis

30
Q

How is the palisade layer adapted to photosynthesis?

A

Has lots of chloroplasts so they are near the top of the leaf, where they can get the most light

31
Q

How is the upper epidermis adapted for photosynthesis?

A

it is transparent so that light can pass through it to the palisade layer

32
Q

How are the xylem and phloem adapted for photosynthesis?

A

They form a network of vascular bundles, provide the leaf with water for photosynthesis and taking away the glucose produced. They also help support the structure

33
Q

How are the epidermal tissues adapted for reducing water loss by evaporation?

A

They are covered with a waxy cuticle, which helps reduce water loss by evaporation

34
Q

How are the tissues of leaves adapted for efficient gas exchange?

A

the lower epidermis has lots of stomata, which lets CO2 diffuse into the leaf.
- the spongy mesophyll tissue contains lots of air spaces which increases the rate of diffusion of gases into and out of the leaf cells

35
Q

How do small leaves or spines help plants like cacti to adapt in extreme conditions?

A

They reduces surface area for water loss by evaporation. spines stop animals eating plants to get water

36
Q

How do curled leaves or hairs help plants like cacti to adapt in extreme conditions?

A

they reduce air flow close to the leaf, trapping water vapour near the surface and reducing diffusion from the leaf to the air. Spines also reduce air flow near the surface of the plant and so do a similar job

37
Q

How do thick waxy cuticles help plants like cacti adapt to extreme conditions?

A

They reduce water loss by evaporation

38
Q

How do thick, fleshy stems help plants like cacti adapt to extreme conditions?

A

They store water

39
Q

How do fewer stomata/stomata that only open at night help plants like cacti adapt to extreme conditions?

A

They reduce water loss by evaporation

40
Q

How do stomata sunken in pits help plants like cacti adapt to extreme conditions?

A

This makes the stomata lower than the surface of the leaf, which reduces air flow close to the stomata. This reduces water loss in the same way as curled leaves or hairs

41
Q

What are auxins?

A

These are plant hormones that control growth at the tips of shoots and roots, They are produced in the tips, They diffuse backwards to stimulate the cell elongation process in the cells just behind the tips

42
Q

What do auxins promote and inhibit?

A

They promote the growth in the shoot, but actually inhibit growth in the root.

43
Q

How are shoots positively phototrophic?

A
  1. When a shoot tip is exposed to light, it accumulates more auxins on the side thats in the shade than the side thats in the light
  2. This makes the cell grow faster on the shaded side and bend towards the light. they can absorb more light for photosynthesis
44
Q

What would shoots growing completely in the dark look like?

A

They would be tall and spindly as the auxins helps them to elongate quickly on all sides. A taller shoot has a better chance of finding light

45
Q

How are shoots negatively phototrophic?

A
  1. When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side
  2. This causes the lower side to grow faster, bending the shoot upwards
46
Q

How are roots positively gravitrophic?

A
  1. A root growing sideways will have more auxins on its lower side
  2. In a root, the extra auxin inhibits growth. This means the cells on top elongate faster, and the root bends downwards
47
Q

How are roots negatively phototrophic?

A

1) If a root starts being exposed to some light, more auxin accumulates on the more shaded side
2) The auxin inhibits cell elongation on the shaded side, so the roots bends downwards, back into the ground

48
Q

What happens to roots that are underground?

A

They arent exposed to light, so they grow downwards due to positive gravitropism

49
Q

How could you investigate the effect of light on the growth of cress seeds

A

1) put some cress seeds in a petri dish
2) Surround the petri dish with black card. Cut a hole in one side of the card only
3) Shine a light into the box through the hole
4) Leave your cress seeds alone for a week until you observe results. (the seedlings should have grown towards the light)

50
Q

How can plant hormones be used as selective weedkillers?

A
  • most weeds in fields are broad-leaved, in contrast to grasses and cereals which have narrow leaves
  • selective weedkillers have been developed from auxins which only affect broad-leaved plants
  • they do this by disrupting the plants growth patterns, which soon kills them
51
Q

How can root powder be used to grow cuttings?

A

By adding root powder, which contains auxins, cuttings are able to produce roots rapidly and start growing as new plants. This allows growers to produce lots of clones of a really good plant quickly

52
Q

How can plant hormones be used to control flower and fruit formation?

A

Gibberelins are hormones that stimulate seed germination, stem growth and flowering. They can be used to make plants flower earlier than they would usually do so, or under conditions in which they wouldnt usually flower
- They could also be used to reduce flower formation, which can improve fruit quality. e.g. apricot treet often produce too many flowers, this causes many fruits to form and as the tree cant support them all, they grow quite small

53
Q

How can plant hormones be used to produce seedless fruit?

A

Fruit only grows on flowering plants that have been pollinated by insects. If the flower isnt pollinated, the fruit and seed may not grow. If plant hormones like gibberelins are applied to unpollinated flowers, the fruit can grow but the seed wont.

54
Q

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

A
  1. the ripening of fruits can be controlled with when they’re still on the plant, or when they’re being transported to shops. This allows the fruit to be picked whn its unripe
  2. A ripening hormone called ethene is then added and the fruit will ripen on its way to the supermarket and be perfect just as it reaches the shelves
55
Q

How can plant hormones be used to control seed germination?

A
  • Lots of seeds wont germinate until theyve been through certain conditions (e.g a period of cold, or of dryness)
  • including gibberelins means that plants can germinate at times of year that they wouldnt normally. It also helps to ensure all the seeds in a batch germinate at the same time

Biology edexcel 9-1 (8 decks)

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