3.4 Plant fertilisation

The pollen grains are on the stigma and the pollen grains germinate and the tube begins to grow and this is usually species specific so the tube will only grow if they are the same species.

The pollen grain (male nucleus) goes down through the pollen tube to the female nucleus (the ovule)
After this has occured 4 things will happen:

1. Pollen grain will fertilise the ovule ------> the formation of a zygote -------> grow into the embryo plant                                                                                                                                                   .
2. The outside of the ovule forms the testa seed coat                                                                             .
3. Inside the ovule in addition to the zygote it will also give the formation of the cotyledons. These are food stores for the seedling. This will support the seedling until it develops its first set of leaves.                                                                                                                                                          .
4. Thickening on the walls of the ovsry so the plant will put a lot of energy there so things like sugars, protein. It will buils these up to form the fruit which is developed from the wall of the ovary/carpel.

3.3b Wind pollination

• Wind pollination is the transfer of pollen grains from the anther to the stigma through air carried by the wind.

The adaptations by wind pollinated plants are:

1. The pollen grains are lightweight so they wind can carry them and also many have a wing feaure to help them get carried by the wind.
2. Exposed anther - anthers will hang well clear of any basic flower structure so that they are exposed to the wind.
3. Exposed stigma - stigma of wind pollinated plants have a really large surface area, a kind of feather like structure to catch pollen grains in the air.

Note that wind pollinated plants do not have                                                                                                     - Coloured petals.                                                                                                                                           - No scent.                                                                                                                                                       - And no nectaries.                                                                                                                                                      

As there would be no point in attracting insects, and doing these things would be a waste of energy.                                                               

3.3a Insect pollination

• in the process of pollinating a flower there has to be a transfer of pollen grains from the anther of one plant to the stigma of another.

• pollen is a small structure which contains the male nuclei. 

• the transfer in a insect pollinated plant takes place by insects and so its necessary for this type of flower to attract the insect into the first flower and then have a reason to go to the second flower.

• if the pollen goes from one plant to another this is what we call cross-pollination.

• when looking at a single flower structure we find the adaptations to attract the insect                       - signals to the insect; coloured petals insects see colour                                                                       - scents to detect                                                                                                                                 - value for the insect -  food- nectaries/ fructose also will use pollen as a source of protein.

• stamen- male part of  plant- made up of anther which produces pollen grains on a stalk called the filament.
• carpel- female part- made up of stigma where pollen grains fall, and the style which connects the style to the ovary, and the ovary which produces eggs/ ovules

2.81 Positive Phototropism.

• Positive phototropism - positive suggests that it is towards light.
•                                    - photo refers to light.
•                                    - tropism refers to growth in response to this light.

•    uniform light coming from all directions means the stem will grow forwards and upwards.

•     however, if the same stem only has light coming from one side (lateral light source) it causes the plant to bend in a grove towards the light.

•  the light on this side causes the opposite side of the stems auxin (plant growth hormone) to grow more which causes the bending.

2.80 Geotropism

• Geotropism= Geo refers to gravity and tropism refers to growth response.
• For example a seed:  
• We find that the embryonic root will grow downwards and this is described as positive geotropism.
• Where as the embryonic shoot will grow upwards towards the soil surface - negative geotropism.

• A different experiment is if you rotate that seed;
• You will see that the embryonic shoot will grow upwards- negative geotropism
• Also that the embryonic root will turn and grow downwards- positive geotropism

2.79 plants respond to stimuli

• Stimuli are changes in the environment. e.g temperature changes or light changes.

• The plant has receptors that detect the stimuli and then turn those into a response.

• The responses often take the form of growth. this type of response to a stimulus is called a tropism.

• Tropisms that involve: light are called phototropism. involve gravity are called geotropism.

• The connection between the receptor and the response usually takes the form of plant hormones sometimes called plant growth regulators.  e.g. Auxin  

2.54 Transpiration

• for evaporation to occur: water (liquid) ---->  water vapour (gas).     and for this to occur you need heat. to get this heat we use sunlight

• water is delivered in from leaf by xylem, and from there it moves through the spongy mesophyll layer and then to just above the stomatal pore. 

• then the gas water vapour diffuses through the stomatal pore through a fairly steep diffusion gradient,  as the water vapour inside the stomatal pore is at 100% humidity and outside the leaf the humidity is less than that and the distance between them is only one cell thick.