Topic 6 - Plant Structures and Functions✅

Describe photosynthetic organisms

• Main producers of food

• Therefore biomass

Describe photosynthesis in plants and algae

• An endothermic reaction (products have more energy than the reactants)

• Uses light energy to react carbon dioxide and water, to produce glucose and oxygen

What are the limiting factors on rate of photosynthesis

• Temperature

• Light intensity

• Carbon dioxide concentration

 

How does concentration of carbon dioxide affect rate of photosynthesis

• Carbon dioxide is needed to make glucose

• As the conc. of carbon dioxide increases, so does the rate of photosynthesis

How does temperature affect rate of photosynthesis

• Temperature increase = rate of photosynthesis increase

• The reaction is controlled by enzymes, which work better at higher temperatures

• At too high of a temperature enzymes can denature and the rate of photosynthesis will decrease

What is the core practical for investigating the effect of light intensity on the rate of photosynthesis METHOD + calculation

• Get a ruler and measure equal distances from a lamp

• Add 20 algal balls to some bottles

• Add indicator solution and put a cap on the bottles

• Measure the pH of all the bottles at the start

• Cover one bottle with foil and put it closest to the lamp

• Turn on the lamp and wait until you see obvious colour changes

• Compare the colours of your bottle with a pH range to get the pH at the end

• Rate of reaction = change in pH / time

Explain how the structure of a root hair cell is adapted to absorb water and mineral ions

• The outer surface has lots of hairs, providing a large surface area so that water and mineral ions can be absorbed quickly

• The hairs have thin cell walls so that the flow of water into the cells is not slowed down

How is xylem adapted to its function

• It contains dead cells with no end walls

  • Forms an empty tube for water to flow through

• Thick side walls are made from lignin, making them rigid and unlikely to burst or collapse

 

How is phloem adapted to its function

• Cells within the phloem are alive

• These cells use energy to transport sucrose around the plant

6.9 - Explain how water and mineral ions are transported through the plant

Transpiration

• Water enters the plant through root hair cells by osmosis

• Water and mineral ions are transported up the plant through the xylem (dead, lignified cells)

  • due to a pressure difference

    • water is pushed up from high pressure in the bottom of the plant to low pressure in the top

• The movement of water also transports dissolved mineral ions

• In the leaf, water evaporates from cells of spongy mesophyll into airscpaes

• Then moves out of stomata by diffusion

 

6.9 - Describe the structure and function of the stomata during transpiration

• Stomata are small pores found on the surface of leaves.

• Guard cells control the opening and closing of the stomata.

• The stomata allow water vapor to escape during transpiration and enable gas exchange (CO₂ in, O₂ out)

• They are on the bottom / underside

6.10 - Describe how sucrose is transported around the plant

Translocation

• Translocation moves sucrose and amino acids

• It happens in the phloem which are alive, hollow, contain sive tubes and companion cells

• Amino acids and sucrose are moved by active transport in the sieve tubes

• Companion cells pump sucrose in or out of the sieve cells, using energy from respiration

 

6.10 - what causes sucrose to move around the plant during translocation

• Pumping sucrose into the sieve tubes increases osmotic pressure

• Water enters the phloem, creating a pressure gradient that moves sucrose solution

• Sucrose flows up to growing shoots, or down to storage organs, depending on the plant's needs

6.11 - Describe how the leaf is adapted for photosynthesis and gas exchange

• Leaves have large surface area to absorb more light

• They are thin, so that there is a short distance for carbon dioxide to diffuse into the leaf cells

• They have stomata, allowing carbon dioxide to diffuse in and oxygen to diffuse out

• They have chlorophyll, which is green because that is the most efficient colour for absorbing light

How does light intensity affect water uptake by a plant

• Greater light intensity makes the stomata wider, increasing transpiration

 

How does air movement affect water uptake by a plant

• Wind moves molecules away from the stomata, reducing rate of transpiration

 

How does temperature affect water uptake by a plant

• Higher temperature makes particles move faster and therefore diffuse faster, increasing transpiration

How to calculate rate for transpiration

• Use a potometer

• Place a plant in a capillary tube in water, then measure the distance travelled by a bubble over 1 minute

• The further the bubble moves, the greater the rate of transpiration

 

How are plants adapted to survive in extreme environments

• Leaf shape and size

  • Many desert plants do not have leaves

  • This reduces the amount of water lost by transpiration

• Waxy cuticle

  • Many leaves have a waxy cuticle, preventing evaporation of water

• Stomata

  • Stomata can be closed, preventing evaporation of water

  • They can open again when carbon dioxide is needed for photosynthesis

How are auxins used as weedkillers

• Weeds are broad-leaved

• Weedkillers can be synthesised so they only affect broad-leaved plants e.g. Weeds

• Weedkillers work because the increased amount of auxin causes the cells to grow too rapidly, resulting in the weed dying

 

How are gibberellins used

• They allow seed germination to occur by breaking seed dormancy

• They allow fruits to grow heavier and larger, increasing yields

• They encourage flowering plants to flower at a faster rate

 

How are ethenes used in fruit ripening

• Fruit is picked and transported when it is not ripe, so it doesn't get damaged

• When it needs to be sold, it is exposed to ethene

• Ethene helps control cell division and stimulates enzyme, resulting in fruit ripening

6.3 - Explain the effect of light intensity on the rate of photosynthesis

• The higher the light intensity, the faster the rate of photosynthesis

What are auxins’ role in positive gravitropism

• Most roots grow towards gravity (positive gravitropism)

• The roots move to the side with less auxin, meaning they grow on the upper side

• This makes the roots bend and grow downwards

• This increases the plant's growth as there is more water and nutrients lower down

What is auxins' role in negative gravitropism

• Most shoots grow away from gravity (negative gravitropism)

• Auxins move towards the lower side, meaning the shoots grow here

• The shoots bend and grow away from the ground

• This helps the plant grow more, as light levels are higher further away from the ground

What is auxins' role in phototropism

• Auxins collect on the shaded side of the plant

• causes cell elongation

• Making the plant bend towards the light

Explain the interactions of temp, light intensity and co2 concentration in limiting the rate of photosynthesis

• Temperature, light intensity and CO2 concentration are limiting factors, because they are factors that prevent a rate from increasing.

• The maximum rate of photosynthesis is controlled by the factor in the shortest supply.

• Once a factor is limiting, changing its supply changes the rate of photosynthesis.

Explain how the rate of photosynthesis is directly proportional to light intensity

• The rate of photosynthesis is directly proportional to light intensity

• This is because the more light you have, the quicker the rate of photosynthesis

• Photosynthesis requires energy, so more energy = faster rate

Explain how the rate of photosynthesis is inversely proportional to the distance from light source

• Rate of photosynthesis is inversely proportional to distance from light source

• As the distance increases, the rate of photosynthesis decreases

  • This is because when the light source is further away from the object, the light intensity it gives off is less

What is the inverse square law calculation

• Light energy is proportional to the square of distance from the light source

  • This means the formula is 1/d²

Explain why root hair cells do not contain chloroplasts

• Root hair cells are under the soil so they have no sunlight on them

• They do not need to photosynthesise, therefore they have no chloroplasts

Why are large leaves an advantage to the plant

• They have a greater surface area

• Means they can catch more sunlight

• This produces glucose by photosynthesis