Topic 6 - Plant Structures And Functions Flashcards
Photosynthesis equation
Carbon Dioxide +water -> Glucose +Oxygen
Photosynthesis reaction type
Endothermic
Factors of photosynthesis rate
Light intensity, Concentration of CO2 and Temperature.
All can limit
Investigate rate of Photosynthesis with light intensity
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.
Light and photosynthesis
Light provides the energy.
It increases directly proportionally until either the CO2 or temperature are the Limiting Factor.
Light intensity =
LUX ∝ 1
—————
Distance^2
Carbon dioxide and photosynthesis
Directly proportional until either Light Intensity and Temperature are limiting
Temperature and photosynthesis
If limiting photosynthesis is slower due to low enzyme activity.
If too high enzymes denature.(45C)
Root hairs
Contain millions of microscopic hairs to increase surface area to maximise water and mineral absorption
Phloem tunes
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.
Xylem
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.
Transpiration
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.
Stomata
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)
Rate of transpiration
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.
Estimate rate of transpiration
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.
Layers of the leaf
Waxy cuticle Upper epidermis Palisade Spongy mesophyll (air gaps) Lower epidermis (guard and stomata)
Waxy cuticle
Reduce water loss.
Upper epidermis
Transparent
Cacti adaptations
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.
Auxin
Hormone that control growth in roots and shoots. Produced at tips and diffuse backwards. Roots = INHIBIT Shoots= PROMOTE Used in phototropism and gravitropism
Shoots and Phototropism
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.
Shoots and gravitropism
NEGATIVE
If it grows sideways gravity causes auxin to collect at the lower side. This causes it to bend away.
Roots Phototropism
If light reaches roots auxin collects on the shaded side. This INHIBITS growth so it bends downwards.
Roots and gravitropism
Sideways growing roots always have auxin on its lower side. This inhibits growth bending downwards.
Investigate phototropism
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
Plant hormones as selective weed killers.
Most weeds are broad leaves.
Developed from auxin which only disrupt growth in broad leaves.
Grow from cuttings with rooting power
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.
Controlling flower and fruit formation
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
Producing seedless fruit.
If gibberellins is applied to unpollinated flower a fruit grows with NO seeds,
Control ripening of fruits.
Ethene is used to ripen fruit for consumption.
So they can be transported unripe so they aren’t easily damaged.
Control seed germination
Many seeds don’t germinate until conditions are correct.
Gibberellins can be used to make seeds germinate all year simultaneously
