1. Green Plants as Organisms

2. Contents Photosynthesis Photosynthesis vs. Respiration Plant Hormones
Commercial Uses of Plant Hormones
Transport and Water Relations

3. Photosynthesis
Photosynthesis is the chemical change which happens in the leaves of green plants. It is the first step towards making food. During this reaction, carbon dioxide and water are converted into glucose and oxygen. The reaction requires energy in the form of sunlight, and chlorophyll must also be present.
Plants are producers – they produce their own food
Plants produce their food via photosynthesis

4. carbon dioxide + water glucose + oxygen
Photosynthesis
Occurs in the leaf
Needs:
Chlorophyll – not used up
CO2 (from the air)
Water (from the soil)
Sunlight energy (any light except green light) – not used up
Produces:
Glucose
Oxygen (waste product)
carbon dioxide + water glucose + oxygen
6CO H2O C6H12O6 + 6O2
chlorophyll + light energy

5. Factors Affecting Photosynthesis
Three factors limit photosynthesis from going any faster:
Light level
Without enough light a plant cannot photosynthesise very fast, even if there is plenty of water and carbon dioxide. Increasing the light intensity will make photosynthesis faster.
2. Carbon dioxide level
Photosynthesis can be limited by the level of carbon dioxide. Even if there is plenty of light a plant cannot photosynthesise if it has run out of carbon dioxide.
3. Temperature.
If it gets too cold the rate of photosynthesis will slow right down. If it gets too hot then plants cease to be able to photosynthesise.

6. Night-time vs. Daytime Daytime: Photosynthesis & Respiration
Night-time: (no sunlight therefore no photosynthesis)
Only respiration

7. Plant Hormones Stem  always grows towards light
Roots  always grow away from light
Auxins are produced in the growing tips of shoots and roots
Auxins respond to light, gravity and moisture
Auxins cause some cells to elongate or grow at a faster rate
Tropism = plant’s response to light, gravity or moisture
Positive tropism = response towards stimulus
Negative tropism = response away from stimulus
controlled by auxins

8. Plant Hormones Geotropism = plant’s response to gravity
Positive geotropism = roots grow towards direction of gravity
Negative geotropism = shoots grow away from direction of gravity
Hydrotropism = plant’s response to water
Positive hydrotropism = shoots always follow direction of water
Phototropism = plant’s response to light
Light destroys auxins
Auxins = plant hormones controlling its growth
Auxins on sunlit side of plant are destroyed,
growth slows…
Growth of plant on shaded side continues
 plant growth leans towards light

9. Commercial Uses of Plant Hormones
Growing cuttings: cuttings are dipped into powder containing growth hormones. Plants are cloned quickly and cheaply
Producing fruit without seeds: Growth hormones sprayed on unpollinated flowers  grow fruit without fertilisation
Ripening fruit: Plant hormone ethene ripens fruit. Sprayed onto unripened fruit during transportation to supermarkets
Increasing size of fruit: e.g. grapes

10. Transport & Water Relations
Plants require water for growth, temperature regulation and to hold themselves up
Transpiration is the loss of water from the leaves by evaporation
Transpiration system:
Water absorbed into roots through root hair cells
Water carried to leaves through xylem vessels
Water evaporates from underside of leaves
Water escapes through holes called stomata
As water evaporates, more is sucked up xylem
Stomata (tiny holes under a leaf allowing it to breathe) open and close to control water loss
Open – O2 and CO2 enter and exit
Closed – Reduce water loss

11. Xylem and Phloem Vessels
Xylem are vein like tissues that transport water and minerals up a plant
Phloem are vein like structures through which food is transported around a plant
Xylem
Phloem
Made of
Dead cells
Living cells
Cell wall thickness
Thick
Thin
Cell wall material
Lignin (rigid)
Cellulose
Permeability
Impermeable
Permeable
Cytoplasm?
None
Cytoplasm lining
Transports…
Water & minerals
Food
Carried to…
Leaves
Growing parts & storage organs
Direction of flow
Upwards
Up and down
Tissue also has…
Fibres
Companion cells

12. Water Provides Support
Green plants rely on cell turgor which is the stiffness given to cell walls to hold themselves up
Cell walls become turgid with water
In woody plants, they do not need cell turgor, but instead rely on the support of the strong, impermeable xylem vessels

13. Summary Photosynthesis: carbon dioxide + water  glucose + oxygen
Limiting factors: temperature, CO2, light intensity
Daytime: respiration & photosynthesis; night-time: respiration
Plant hormone, auxin, responds to light, gravity and moisture
Light destroys auxin
Auxin speeds up plant growth
Water travels around the plant via the transpiration system
Xylem and phloem vessels transport water, minerals and food
Water is needed in green plants for structure and support