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IGCSE Biology > Topic 6 Gas Exchange + Nutrition in Plants > Flashcards

Topic 6 Gas Exchange + Nutrition in Plants Flashcards

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1
Q

What is the word equation for photosynthesis?

A

Carbon dioxide + water -> glucose + oxygen

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2
Q

What is the chemical equation for photosynthesis?

A

6CO2 + 6H2O -> C6H12O6 + 6O2

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3
Q

What is the role of diffusion in gas exchange during photosynthesis?

A
  • carbon dioxide diffuses DOWN concentration gradient from HIGH concentration (outside leaf) to LOW concentration (inside leaf)
  • oxygen diffuses down concentration gradient from high concentration (inside leaf) to low concentration (outside leaf)
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4
Q

Why is the carbon dioxide concentration always low inside photosynthesising cells?

A
  • cells use carbon dioxide in photosynthesis

- > conc always low

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5
Q

How is the structure of the leaf adapted for gas exchange?

A
  1. Stomata + guard cells allow diffusion of gases in and out of leaf
  2. Leaf shape = thin -> decreases diffusion distance
  3. Spongy mesophyll cells have large SA + moist surfaces for fast diffusion
  4. Air spaces increase SA
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6
Q

Why does a leaf have a waxy underside?

A

Prevents excess water loss

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7
Q

How is the structure of the leaf adapted for photosynthesis?

A
  • maximum number of palisade cells packed in to absorb sunlight
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8
Q

What happens when guard cells gain H2O by osmosis?

A
  • expand + curve out

- stomata opens -> allows for gas exchange

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9
Q

What happens when guard cells lose water via osmosis?

A
  • stomata closes
  • gas exchange can no longer occur
  • water can’t be lost
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10
Q

What is the net exchange of carbon dioxide and oxygen during the day?

A
  • depends on light intensity but higher rate of photosynthesis
  • > net diffusion of carbon dioxide into plant + net diffusion of oxygen out of plant during day
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11
Q

What is the net exchange of carbon dioxide and oxygen during the night?

A
  • plants only respire (no sunlight)

- > net diffusion of oxygen into plant + net diffusion carbon dioxide out of plant

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12
Q

Cormmss method for investigating effect of light on net gas exchange from leaf using hydrogen carbonate indicator

A

C - change availability of light for each boiling tube (foil, no foil etc)

O - plant used will be pondweed - same species age + length

R - repeat experiment 3 times to ensure reliability

M - observe change in hydrogen carbonate indicator

M - after 30 mins

S - control vol of hydrogen carbonate indicator / no of leaves / temp of environment

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13
Q

In a test tube containing a plant, what colour would the hydrogen carbonate indicator be after it was exposed to light?

A

Purple - low CO2 levels

Carbon dioxide + water -> oxygen + glucose

RELEASE of oxygen in photosynthesis

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14
Q

Why would a control test tube for the hydrogen carbonate experiment be included?

A
  • measures baseline levels of co2 to compare to other results
  • makes sure that pondweed was causing the colour changes
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15
Q

How would you know which test tube was kept in bright light?

A
  • purple

- > higher levels of photosynthesis -> less co2 released

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16
Q

What colour is the test tube that was kept in the dark and why?

A
  • yellow
  • > higher levels of respiration -> co2 released
  • photosynthesis could not be carried out
17
Q

What test tube is at compensation point?

A
  • orange
  • > equal levels of co2 and o2 (remember however, that OXYGEN DOES NOT AFFECT the indicator)
  • > thus rate of photosynthesis = rate of respiration
18
Q

During photosynthesis what is light energy converted into?

A

Chemical energy

By chloroplasts

19
Q

How does light intensity affect photosynthesis?

A

Increases the rate of photosynthesis -> more energy for reaction
Graph will be linear then level off (becoming constant) as another factor limits the rate

20
Q

How does carbon dioxide concentration affect photosynthesis?

A

Increases the rate of photosynthesis -> more reactants

Graph will be linear then level off (becoming constant) as another factor limits the rate

21
Q

How does temperature affect photosynthesis?

A

Increase in temp up to optimum -> increase rate of photosynthesis
After optimum -> decreases

Increase in kinetic energy -> more successful collisions between active site + substrates

After optimum -> enzymes denature -> active site changes shape + no longer complementary to substrate

Too hot -> too much water loss

Graph peaks at optimum and then decreases

22
Q

What is a limiting factor?

A

Factor present in an environment that controls a process

23
Q

How do chloroplasts affect photosynthesis?

A

More chloroplasts (contain chlorophyll which absorbs light energy) increases rate

24
Q

Why can a starch test show whether the leaf is photosynthesising?

A

Starch is made from glucose -> a product of photosynthesis

25
Q

Why do you put the leaf in boiling water and then ethanol and then water before the starch experiment?

A
  • boiling water kills tissues + breaks down cell walls
  • ethanol removes chlorophyll -> colour changes can be seen more clearly
  • wash in water to soften leaf tissue -> more permeable + allows colour change to be observed more clearly
26
Q

What would be the results for starch test on:

  • leaf with strip of paper over it
  • variegated leaf
A
  • leaf covered by paper will turn orange brown -> starch not present -> no sunlight -> no photosynthesis occurring
  • the rest would be blue black
  • the green part of variegated leaf = blue black (starch present, chlorophyll present, photosynthesis is occurring)
  • white part = orange brown (not present, not chlorophyll)
27
Q

Cormms for light and starch test?

A

C - light / no light

O - leaves from same species, age, size of plant

R - repeat x 3 for reliability

M -observe colour change of leaf when iodine is applied

M - after 1 day collect results

S - control room temp

28
Q

Method for investigating affect of carbon dioxide concentration with starch?

A
  1. Destarch two identical plants
  2. Place them in plastic bags
  3. Place saturated sodium hydrogen carbonate (gives out co2) in one bag
  4. Place soda lime (absorbs co2) in other bag
  5. Leave in bright light for a day
  6. Test a leaf from each plant with iodine
29
Q

What are the results for the starch test for co2 conc?

A

Plant with sodium hydrogen carbonate turns blue / black -> starch in leaf -> photosynthesis -> glucose produced

Plant with soda lime turns orange / brown -> no starch in leaf -> photosynthesis not occurring (no co2 for it) -> glucose not produced

30
Q

How do you investigate affect of light intensity on photosynthesis? By measuring carbon dioxide released?

A
  1. Fill boiling tube with water
  2. Add pondweed
  3. Place the lamp at fixed distance from tube, leave until bubbles can be seen
  4. Count number of bubbles released in 5 minutes at each distance
  5. Repeat + calculate a mean for each distance
31
Q

How could you make the method more accurate for measuring carbon dioxide versus light intensity?

A
  • measuring vol of gas released with an inverted measuring cylinder / gas syringe since bubbles = diff sizes
  • may contain different vols of gas
32
Q

What do plants do with glucose?

A
  1. Convert -> insoluble starch for storage
  2. Convert -> fat + oil for cytoplasm
  3. Makes cellulose for cell walls
  4. Combines w nitrates -> amino acids (to make proteins)
  5. Converted -> sucrose -> transport around plant in phloem
33
Q

What are nitrates needed for?

A

Amino acids + proteins

-> lack of nitrates = poor plant growth

34
Q

What is magnesium needed for?

A

Chlorophyll

-> lack of magnesium= yellow plant

35
Q

What are phosphates for?

A

DNA = ATP

-> lack of phosphates = poor root growth + discoloured leaves

36
Q

What is potassium for?

A

Helps photosynthesis + respiration enzymes function

-> lack of potassium : discoloured leaves, poor flower + fruit growth

IGCSE Biology (22 decks)

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