Topic 6 - Plant Structures And Functions

Question 1

Photosynthesis equation

Answer 1

Carbon Dioxide +water -> Glucose +Oxygen

Question 2

Photosynthesis reaction type

Answer 2

Endothermic

Question 3

Factors of photosynthesis rate

Answer 3

Light intensity, Concentration of CO2 and Temperature.

All can limit

Question 4

Investigate rate of Photosynthesis with light intensity

Answer 4

Use an aquatic plant in water. Add Sodium Hydrogencarbonate to supply CO2. CONTROL: Temp, CO2, Water vol.
Use a white light at a set distance.
Wait a period of time.
Oxygen released will be collected in gas syringe.
Measure oxygen.
Repeat at different distances.

Question 5

Light and photosynthesis

Answer 5

Light provides the energy.

It increases directly proportionally until either the CO2 or temperature are the Limiting Factor.

Question 6

Light intensity =

Answer 6

LUX ∝ 1
—————
Distance^2

Question 7

Carbon dioxide and photosynthesis

Answer 7

Directly proportional until either Light Intensity and Temperature are limiting

Question 8

Temperature and photosynthesis

Answer 8

If limiting photosynthesis is slower due to low enzyme activity.
If too high enzymes denature.(45C)

Question 9

Root hairs

Answer 9

Contain millions of microscopic hairs to increase surface area to maximise water and mineral absorption

Question 10

Phloem tunes

Answer 10

Elongated columns with pores at end walls to allow flow.
Transport sucrose (food) for immediate use or storage,
Uses translocation requiring energy from respiration. Both directions.

Question 11

Xylem

Answer 11

Made of dead cells joined end to end without walls. Strengthened with lignin.
Carry water and mineral ions from roots to stem and leaves with transpiration.

Question 12

Transpiration

Answer 12

Loss of water by evaporation and diffusion. Mostly at leaves.
Loss of water in leaves causes water to be drawn through xylem to replace it. Meaning there is a constant flow. Brings minerals with it.

Question 13

Stomata

Answer 13

Gas exchange. Small pores on the surface. Allow CO2, water vapour and oxygen to diffuse. Transpiration is a side-effect, diffuse out due to difference in pressure.
Guard cells change the shape:
Turgid - open (allow transpiration)
Flaccid- Closed (prevent water loss)

Question 14

Rate of transpiration

Answer 14

Light Intensity - brighter = greater rate due to stomata stay open when photosynthesising
Temperature- Higher = more evaporation
Air Flow- If low the vapour surrounds leaf equalising the pressure inside and outside reducing diffusion.

Question 15

Estimate rate of transpiration

Answer 15

Using a potometer. Measures water uptake assuming it’s related to loss. The bubble of air is drawn to the plant over a period of time. Calculate rate.

Question 16

Layers of the leaf

Answer 16

Waxy cuticle
Upper epidermis
Palisade 
Spongy mesophyll (air gaps)
Lower epidermis (guard and stomata)

Question 17

Waxy cuticle

Answer 17

Reduce water loss.

Question 18

Upper epidermis

Answer 18

Transparent

Question 19

Cacti adaptations

Answer 19

Small leaves (spines, reduce surface area, prevent animals eating)
Curled leaves - reduce air flow to trap vapour around leaf to reduce diffusion
Waxy Cuticle- reduce water loss by evap.
Thick, fleshy stem stores water.
Fewer stomata that only open at night.
Stomata in pits to reduce air flow.

Question 20

Auxin

Answer 20

Hormone that control growth in roots and shoots.
Produced at tips and diffuse backwards.
Roots = INHIBIT
Shoots= PROMOTE
Used in phototropism and gravitropism

Question 21

Shoots and Phototropism

Answer 21

POSITIVE
If shoot is exposed to light it accumulates auxin on the shady side.
Cells grow faster on shaded side. So it will bend towards light.
Increasing photosynthesis for growth.

Question 22

Shoots and gravitropism

Answer 22

NEGATIVE

If it grows sideways gravity causes auxin to collect at the lower side. This causes it to bend away.

Question 23

Roots Phototropism

Answer 23

If light reaches roots auxin collects on the shaded side. This INHIBITS growth so it bends downwards.

Question 24

Roots and gravitropism

Answer 24

Sideways growing roots always have auxin on its lower side. This inhibits growth bending downwards.

Question 25

Investigate phototropism

Answer 25

Cress seeds in a Petri dish (surrounded by black card) lined with moist filter paper.
Cut a hole and shine light through. Observe their growth

Question 26

Plant hormones as selective weed killers.

Answer 26

Most weeds are broad leaves.

Developed from auxin which only disrupt growth in broad leaves.

Question 27

Grow from cuttings with rooting power

Answer 27

Where a part has been cut off.

If you place cutting in soil with rooting powder (auxins) they produce roots and grow to a new plant as a clone.

Question 28

Controlling flower and fruit formation

Answer 28

Gibberellins stimulate seed germination (stem growth and flowering).
They make plants flower earlier or under certain conditions.

Also can reduce flower formation to improve fruit quality

Question 29

Producing seedless fruit.

Answer 29

If gibberellins is applied to unpollinated flower a fruit grows with NO seeds,

Question 30

Control ripening of fruits.

Answer 30

Ethene is used to ripen fruit for consumption.

So they can be transported unripe so they aren’t easily damaged.

Question 31

Control seed germination

Answer 31

Many seeds don’t germinate until conditions are correct.

Gibberellins can be used to make seeds germinate all year simultaneously