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

Photosynthesis

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

Plants use photosynthesis to make their own food

YouTube - Photosynthesis Song

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)

LeavesWaterproof layer protects leaf

Most photosynthesis occurs here (lots of chloroplasts)

Carry water

Carry food

vein

Hole that lets carbon dioxide in and oxygen out by diffusion

Controls size of stoma (plural = stomata)

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.

Today the atmosphere is

78% Nitrogen

21% oxygen

0.9% Argon

About 0.04 % CO2

Variable amounts of water vapour

Changing atmosphere

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.