CB6: Plants Flashcards
Why are some leaves darker?
They have more chloroplasts. This is because they aren’t used to recieving as much light.
What are the signs that a leaf is recieving less light?
It is larger and darker.
What is the name of the chemical that makes leaves green and what can it be found in?
Chlorophyll. In chloroplasts.
What is the name of the pigment that makes some plants orange?
Carotenoids
Why do plants have different pigments?
To maximise their usage of the solar energy that they recieve
Is photosynthesis exothermic or endothermic?
Endothermic. It needs energy.
What is the word equation and the balanced symbol equation for photosynthesis?
6CO2 + 6H2O —-(sunlight and chlorophyll)—-> C6H12O6 + 6O2
carbon dioxide + water -> glucose + oxygen
How is energy stored in a plant?
starch
Why do plants photosynthesise?
to get energy, which is used up in respiration
What is Fick’s law?
Rate of diffusion is roughly equal to (surface area * conc diff)/thickness of membrane
Why are leaves thin?
So that gases can reach cells easily
Why are leaves veiny?
to carry water to the cells and carry glucose away
Where are the stomata?
the underside of the leaf
What do stomata do?
they move gas in and out
How are cacti adapted?
- Some are whiter because they have densely packed spikes. This means that they stay cool to stop their enzymes denaturing.
- Fat cacti lose less water because they have a lower SA to volume ratio
- Leaves evolved into spikes to reduce SA so that they don’t dry out as quickly
- Only the stem contains chlorophyll
- Stem is rounded to reduce SA
- Long roots to reach water deep down
- Stem stores water during droughts
How are insect-pollinated flowers adapted?
- Flowers are bright leaves. They attract insects.
- Flowers smell good to attract insects.
- Bees accidentally brush pollen from the anthers to the stigma
- Nectar is made at the bottom of the petals
- The pollen is spiky to stick to insects
How are wind-pollinated flowers adapted?
- Anthers hanging out of the flower so they allow the wind to carry the pollen away. It falls onto stigma eventually.
- The pollen is round so it is aerodynamic.
Limiting factors of photosynthesis
- Amount of chloroplasts (contain chlorophyll)
- Light intensity
- Moisture in the air
- CO2 concentration
- Temperature
How do you test leaves for starch?
Simplified:
1. Boil in water to break down the cell wall
2. Boil in ethanol to remove colour
3. Add iodine which changes colour and tests for starch
More detail:
1. Boil 200ml water over blue flame
2. Add the leaf and leave it for 2 mins
3. Turn off the bunsen burner. Pick up the leaf.
4. Add to a test tube with ethanol to remove the colour
5. Place it back in the water with the bunsen burner off for ~2 mins
6. Take out the leaf and put it on a white tile. Dunk in cold water if it’s brittle.
7. Add iodine. Turns black if starch is present.
How do you measure the rate of photosynthesis?
Use an elodea bubbler.
- Put some pondweed in water and baking soda. It will photosynthesise.
- Oxygen produced can be collected in a test tube.
- Rate can be measured by counting the bubbles
THIS IS A BAD EXPERIMENT THOUGH:
- innacurate - a gas syringe could be used to measure more precisely.
Translocation
movement of sugars and other chemicals (assimilate) made by plant cells along the phloem.
assimilate
a complex solution (eg: sap)
main assimilate
sucrose (a type of sugar)
xylem
transports water from the root to the leaf
phloem
transports sucrose to basically wherever
What are sources and sinks?
source: where sucrose is created and released into the phloem
sink: where sucrose is used or removed from the phloem
How does sugar get into the phloem?
- Companion cells use ATP to actively transport hydrogen ions into the surrounding tissue. This creates a diffusion gradient with a high concentration of hydrogen ions outside the companion cells.
- Hydrogen ions move back into the companion cells using co-transporter proteins and bring sucrose with them. The concentration of sucrose in the companion cells increases.
- Sucrose moves from the companion cells to the sieve tube elements using the plasmodesmata.
transpiration is…
How water passes up the stem
What affects the rate of transpiration?
- Temperature
- Size of the leaf (SA)
- Water concentration (humidity)
- Wind speed
How do you measure the rate of transpiration?
Using a potometer
Nitrate (NO3-) in fertiliser?
used for: making proteins, enzymes, and other essential molecules
deficiency: causes pale leaves because it can’t make chlorophyll
fertiliser: can pollute groundwater
Phosphate (PO4-) in fertiliser?
used for: catalyst and energy transfer
deficiency: leaves become purple. leaves become necrotic. needed for healthy growth
fertiliser: can lead to better soil
Potassium cations (K+) in fertiliser?
used for: controls water uptake and photosynthesis
deficiency: poor flowering or fruiting. extreme moisture causes level of O2 in the soil to decrease
fertiliser: can increase growth, can cause Mg2+ deficiency
Magnesium cations (Mg2+) in fertiliser?
used for: making chlorophyll
deficiency: limited growth, leaves yellowing. lack of energy due to no chlorophyll
fertiliser: can lead to Ca and K deficiencies, essential for growth
What is a tropism?
a response developed by plants to make sure they grow towards adequate sources of light and water
What are the two kinds of tropisms?
positive tropism: plant grows towards stimulus
negative tropism: plant grows away from stimulus
What is phototropism?
growth towards light
What are auxins?
a type of plant hormone (eg: IAA)
What does an unqeual distribution of auxin cause?
unequal growth
What do auxins do?
control the rates of elongation in cells and growth in stems and roots.
What does sunlight do to auxins?
Breaks them down
What does high concentrations of auxins do?
cells in stems grow more, cells in roots grow less
What is gravitropism?
response to gravity
What is chemitropism?
response to chemicals
What is thigmotropism?
response to touch
What is hydrotropism?
response to water
