1.17 – Energy Flow and Photosynthesis

Homework Pg. 76 #2-6

Light from the sun is the ultimate source of energy for most living things

Organisms can’t use light directly. They have to capture solar energy and store it as chemical energy in carbohydrate molecules, such as glucose, and then transfer the energy from glucose to ATP.

The absorption of light energy and the production of glucose occur though photosynthesisAutotrophs – an organism (such as a plant) that obtains energy directly from light • they make their own food

Heterotrophs – an organism (such as an animal) that obtains energy by eating other organisms• they can’t make their own food

Photosynthesis: The Process

Photosynthesis occurs in the chloroplasts, which are found in the leaves of plants

Chloroplasts contain an inner and outer membrane and have little compartments called thylakoids.

Thylakoids stack on top of each other to form a structure called a granum.

A protein-rich fluid called stroma fills the rest of the space.

Chlorophyll, a green pigment, is found in the thylakoid membranes.

Chlorophyll molecules absorb light energy and begin the process of photosynthesis.

The equation for photosynthesis is:6 CO2(g) + 6 H2O(l) + light energy → C6H12O6(aq) + 6 O2(g)

Photosynthesis occurs in 2 steps:

1. The Light Reactions• Require light in order to happen• Photosynthesis begins when the chlorophyll

molecules in the thylakoid membranes trap light and transfer its energy to ATP molecules

2. The Calvin Cycle• Reactions of photosynthesis in which carbon

dioxide molecules are used to produce glucose• The carbon atoms in glucose come from the carbon

atoms in CO2

• The ATP molecules made in the light reactions are required for the Calvin Cycle to occur– This energy is transferred to the glucose that is

produced• This part of the reaction can occur without sunlight,

so it is referred to as the dark reactions

Accessory PigmentsA multicoloured pigment in chloroplast membranes that assists chlorophyll in absorbing light E• Ex. Carotenoids (orange), xanthophylls (yellow), anthocyanin

(red)

In spring and summer, leaves look green because of the high [chlorophyll] in the chloroplast membranes

When temperatures cool down, leaves stop producing chlorophyll and the molecules of chlorophyll that are already there start to break down• This allows the bright colours of the accessory pigments to

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