WHERE DOES OUR FOOD COME FROM?

Photosynthesis Photosynthesis is the process whereby light energy is absorbed and glucose is made in a plant

Photosynthesis occurs in plants and is coupled with cellular respiration to produce cellular energy (ATP) Photosynthesis can also occur in photosynthetic bacteria and plantlike protists!

Photosynthesis occurs in green plants. Cellular respiration occurs in all living organisms. Photosythesis and cellular respiration are complementary reactions.

There are two types of organisms on this planet: Autotrophs organisms that can feed themselves, ex. green plants b) Heterotrophs - organisms that feed on others, ex. humans and other animals

Where does photosynthesis take place? Photosynthesis occurs in all parts of a plant, but the leaves are specialized for this purpose.

Inside a Leaf:

Photosynthesis occurs in the chloroplast Chloroplast: a plant cell organelle where photosynthesis occurs - each chloroplast contains many molecules of chlorophyll, the green pigment that absorbs light energy.

The Structure of a Chloroplast: The membrane-bound stacks of thylakoids contain many chlorophyll molecules

When chlorophyll molecules absorb light energy they begin the process of photosynthesis:

The Reaction of Photosynthesis: 6 CO2 + 6H2O C6H12O6 + 6 O2

The Two Reactions of Photosynthesis: The Light Reaction - photosynthesis begins when chlorophyll molecules in the chloroplast trap light energy and transfer this energy to ATP molecules - because this reaction depends on light, it is also called the “Light-Dependent Reaction”

B) The Calvin Cycle - ATP from the light reaction is used to make glucose - This reaction depends on the ATP from the light reaction!

C6H12O6

Overall:

But…Why do plants change colour if chlorophyll is green?? Leaves use more than one pigment to help them absorb more light energy. Accessory pigments: multicoloured pigments in chloroplast membranes that assist chlorophyll in absorbing light energy

When temperatures cool off leaves stop producing chlorophyll When temperatures cool off leaves stop producing chlorophyll. This allows other colours to show: Carotenoids, which produce yellow, orange, and brown colors Anthocyanins, which produce reds, violets, and purples Xanthophylls, which produce yellow

Some unique plants: 1) Parasitic plants - some photosynthesize & obtain some nutrients from others ex. mistletoe is photosynthetic but  obtains water & minerals via projections into the trunk of the tree it is parasitizing!!!

2) Carnivorous plants - photosynthesize - have modifiied leaves to trap & digest insects to obtain some of their nitrogen & other minerals                  ex. Venus fly trap         * enables these plants to live in mineral poor soils! *

Homework! Name three large groups of organisms that carry out photosynthesis. Distinguish between autotrophs and heterotrophs. Provide one example of each. a) What is the name of the pigment molecule in green plants that begins the reaction of photosynthesis? b) What are accessory pigments? Name them and give their colour 5. Write the overall equation for photosynthesis.