Photosynthesis
Photosynthesis is a chemical reaction that plants use to make their food (glucose) using energy from the sun. Photosynthesis occurs within the leaves. The leaves then use the glucose to generate other useful substances and to obtain energy through respiration. Photosynthesis only occurs in the light.

The word equation for Photosynthesis is:

The balanced chemical equation is: 6CO₂ + 6H₂O --> C₆H₁₂O₆ + 6O₂

**Make sure you learn both these equations - it is highly likely that you will be asked these in your exam**

The Process of Photosynthesis
Read the following passage carefully. There will be questions at the end for you to answer.

The process of photosynthesis takes place in the leaves. This means that all the different components of the chemical reaction must be present within the leaves for Photosynthesis to occur. Carbon Dioxide enters the leaf through tiny holes on the under surface of the leaf. These holes are called stomata. 

Chloroplasts containing chlorophyll occur in their greatest numbers on the upper side of the leaf in palisade cells. The chlorophyll is a green pigment that absorbs the energy from sunlight so that photosynthesis can take place.

Inside the leaf there are veins that are continuous extensions of the stems and roots. These veins contain xylem and phloem, two types of plant tissue that transport certain substances throughout the plant. The xylem transports water to the leaves from the roots since water is needed for photosynthesis to occur.

The phloem transports glucose (created by photosynthesis) away from the leaves and around the plant to where the glucose is most needed. This tends to be the growing areas (the buds) and the storage areas (the roots).

The oxygen that is produced as a result of photosynthesis leaves the plant through the stomata through the process of diffusion. 

The rate of photosynthesis can be affected by the availability of certain key components. For example if there is more light then the rate of photosynthesis will increase. The same is true if there is a greater concentration of carbon dioxide.

Temperature also affects the rate of photosynthesis - the optimum temperature for photosynthesis to occur is 30 degrees centigrade. If the temperature is greater than 45 degrees centigrade the rate of photosynthesis will slow down.

Questions
Hopefully you now have a greater understanding of Photosynthesis. Can you answer the following questions based on the passage above?

1) In which part of the plant does photosynthesis occur?

2) What four components do you need for photosynthesis to occur?

3) What are stomata?

4) How is oxygen removed from the plant?

5) What does the xylem transport?

6) Name two key areas where glucose is transported to.

7) What plant tissue is responsible for transporting the glucose around the plant?

8) Name two factors that can lead to a change in rate of photosynthesis.

9) Chloroplasts are present in which cells on the upper side of leaves?

10) Which component absorbs the energy from sunlight for photosynthesis to occur? Chlorophyll.

Plant Reproduction
Using the scroll down bars, can you correctly name all the parts of the flower labelled below.

Plant Reproduction, Fertilisation and Pollination

Read the following passage carefully. There will be questions at the end for you to answer.

Consider the picture above. 
Carpel is the name given to the female parts of the flower. These are the stigma, the style and the ovary. Stamen is the name given to the male parts of the flower. These are the anther, the pollen grains and the filament.
The anther produces pollen grains, which are the male sex cell. These pollen grains (through pollination) will land on the stigma of a flower and grow a pollen tube through the style to the ovule (the female sex cell) within the ovary.
Once the pollen tube reaches the ovule, a nucleus of the male cell can fuse with a nucleus in the female cell allowing fertilisation to occur. Then the ovary turns into a fruit and the ovule will grow into a seed.

The way in which a pollen grain is transferred to a stigma is called Pollination. It is interesting to note that plants can either self-pollinate (pollen grain transfers to the stigma of the same plant) or cross-pollinate (pollen grain transfer to stigma of another plant).
When cross-pollination occurs the pollen grain must obviously be moved to another area where it can attach itself to a stigma. Cross-pollination occurs in two ways - either by wind or by insects.

In order to attract insects to carry the pollen grains away, flowers normally have bright coloured petals to draw the insects in. The pollen grains are sticky and stick to the legs of insects that then carry the grains away where they will attach to the stigma (which is also sticky). Flowers that depend on insect pollination have other ways of attracting insects such as scented flowers or sugary nectar.

Flowers that are dependent on wind pollination have no need to attract insects. Hence the petals on these flowers tend to be not so brightly coloured and generally have no scent or nectar. However in order to have the best possible chance of pollination, these plants will tend to have long filaments which allow the anther to hang outside of the flower so that the wind can catch and carry the pollen grains to a stigma.

Hopefully the above passage would have given you a greater understanding of fertilisation and pollination. Can you now answer the questions below?

(For these questions, blank space and a separate box where answer will appear)
 

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