Do now! Can you stick the target sheets in please? Can you then fill out the first column of the target sheet? YouTube - Human ' Treeman ' begs for help as he turns into a tree.

9c – Plants and photosynthesis

Plants use photosynthesis to make their own food Water + carbon dioxide (+ light energy) glucose + oxygen Reactants Products Chlorophyll absorbs light energy to make photosynthesis happen Most of the glucose is then turned into starch by the plant Starch is an insoluble storage material Photosynthesis only happens when it is light YouTube - Photosynthesis Song Plants use photosynthesis to make their own food

Plants respire too! glucose + oxygen Water + carbon dioxide (+ energy) Reactants Products Aerobic respiration (uses oxygen) Happens all the time Overall plants produce more oxygen by photosynthesis than they use by respiration YouTube - Plant Physiology: Respiration (Britannica.com)

Leaves Waterproof layer protects leaf Most photosynthesis occurs here (lots of chloroplasts) Carry water vein Carry food Controls size of stoma (plural = stomata) Hole that lets carbon dioxide in and oxygen out by diffusion

Leaves Thin so that CO2 does not have to travel far to palisade cells Photosynthesis faster in more light Photosynthesis faster by increasing CO2 concentration Less light = need for bigger leaves

Use of glucose by plants Glucose molecules can be joined together (polymerisation) to make starch (a food store) or cellulose (cell walls) or fats Glucose molecule

Use of glucose by plants Glucose can also be turned into amino acids by combining with Nitrogen from nitrates. Amino acids can be joined together to make proteins

Roots Root hair cells have a large surface area to absorb more water

Xylem The water travels up xylem tubes to the leaves. The water also contains minerals salts.

Phloem tubes These transport dissolved glucose around the plant

Mineral salts Nitrates needed to make proteins – too little = poor growth Phosphates needed to make cell membranes and for root growth Potassium needed to help enzymes for photosynthesis and respiration – too little = yellow leaves

Changing atmosphere When the earth formed (around 4600 million years ago) the atmosphere was mainly carbon dioxide (produced by volcanoes)

Changing atmosphere Around 3800 million years ago, algae evolved, which used photosynthesis to turn CO2 into glucose and oxygen. The oxygen would have been poisonous to other organisms living at the time.

Changing atmosphere Today the atmosphere is 78% Nitrogen 21% oxygen 0.9% Argon About 0.04 % CO2 Variable amounts of water vapour

Changing atmosphere The composition of the atmosphere continues to change……WHY?

Homework Read pages 26 to 35 of your book AT LEAST TWICE, due Friday 15th April I wonder why he’s asked us to do that? He must have a very good reason.