Gr 9 Second termHow plants work

Plants produce there own food (glucose) by photosynthesis

Carbon dioxide + Water(+ light energy) Glucose+Oxygen [ in the presence of chlorophyl]

Plants:Light energy potential energy

Animals get energy from plants

Predators and other meat eating animals get their energy from animals that originally got it from plants.

Carbon dioxide +Water(+ light energy)Glucose + Oxygen

Photosynthesis

Energy is taken up during photosynthesis. It is therefore an example of an endothermic chemical reaction.

Functions of plants:

Plants supply food to humans and all other animals.

Plants remove carbon dioxide from the atmosphere.

Plants release oxygen to the atmosphere.

Plants supply shelter/habitat to animals.

Many medicines are made from plants

Wood from plants are used to make furniture and to build houses.

Wood is used as a fuel.

Parts of the plant

rootsstemleavesFlower / fruits

Functions of the organs of a plant:

a) Root hair cells absorp water

and minerals from the soil.

b) Roots anchor the plant in the soil.

Roots

a) Keep the plant up straight for sunlight to reach the leaves.

b) Stems contain small tubes that transport water and dissolved minerals (called xylem) from the roots to the rest of the plant and food (transported in phloem) from the leaves to the rest of the plant.

Stems

Leaves-Leaves are specialised organs for photosynhesis. They produce food (simple sugars/glucose) that the plant needs for it’s life processes (MRS GREN).

Leaves are green because the cellscontain a molecule or colour pigment called chlorophyll (in the chloroplasts).

The palisade cells are specialised cells for photosynthesis. They are found in the top layer of a leaf.

The xylem, which transports water and dissolved minerals and the phloem, which transports food around the plant, form the veins of a leaf

Stomata are little holes which are found mainly on the bottom of a leaf. Exchange of three gasses namely carbon dioxide, oxygen and water vapour takes place through the stomata.

Flowers

Specialised organs for reproduction. They contain both male (anthers) and female (carpel) parts that are responsible for sexual reproduction in plants.

What do plants need to grow well?

Seeds need oxygen, water and warmth to germinate.

Plants need carbon dioxide, water, sunlight, soil with a specific pH and minerals ( such as phosphates, potassium, nitrogen and magnesium) to grow well

Farmers and gardeners add fertilizers or compost to the soil to supplement the amount of minerals. The use of too many fertilizers can damage the environment. We call this process eutrophication.

The burning of fossil fuels result in the release of sulphur dioxide and nitrogen oxide. These two oxides react with the water in rain drops to form sulphuric and nitric acid. As a result of this the pH of rain drops and the rain becomes very acidic. It can be as acidic as vinegar. Acid rain is harmful to metal, soil, stone and plants.

What happens to the glucose (sugar) that is made during photosynthesis?

As previously said, glucose(sugar) is made during photosynthesis. The plant uses it for it’s own life processes.

The phloem transports it through the plant. Excess glucose is binded together to form starch.

The starch is stored in the plant, mainly by the roots.Starch in a photosynhesising plant can already be detected in the leaves.

Test for starchMethod Reason

Step 1: Put a leaf in boiling water for about 5 minute, until it is soft.

To break down the cell walls so chemicals can enter the cell.

Step 2: Put the leaf in a test tube with ethanol for a while.

To remove the green pigment (chlorophyl). This is for us, to more clearly see a colour change when we add iodine.

Test for starchMethod Reason

Step 3: Rinse the leaf in water.

To make it soft again.

Step 4: Spread the leaf out on a white tile/saucer/petri dish.

Step 5: Drop a few drops of iodine on the leaf

To stain any starch, if present. Turns blue/black if starch is present. Stays yellow/brown if no starch is present.

A leaf covered with iodine turns black due to the presence of starch

Is light needed for photosynhesis?

If plants are kept in a dark cupboard for longer than 24 hours they do not have anymore stored starch in their leaves. The starch is broken down into sugar. The plant uses the sugar for it’s own life processes (MRS GREN).

Plan an investigation to determine if sunlight is needed for photosynhesis.

Aim of the investigation

To determine if sunlight is needed for photosynthesis.

A. The planning of an investigation consists of the following steps:

a) Find the variables.b) Formulate a hypothesis for the investigation.c) Write down the method, step-by-step, that you

are going to follow. d) How are you going to record your results?e) Which safety measures will you have to keep in

mind?f) What do you predict (think) your results are

going to be? Explain your answer by using scientific knowledge.

Is oxygen released during photosynthesis?

a) What are the variables in this investigation?b) Formulate a hypothesis for the investigation.c) Write down the method, step-by-step, that they are going to follow.d) How do we know that the gas released is oxygen?e) Why is the release of oxygen during photosynthesis so important?f) Study the above figures. Write down the results and the conclusion for this investigation.

Water in plantsPlants need water for : a) Transport of substances to and through

the plant.

b) Cooling down the plant.

c) Supporting the soft parts, to keep them firm and upright.

d) Photosynthesis

e) Chemical reactions in the plant cells.

Water enters the plant through the specialised root hair cells. It moves through the roots, stems and leaves in the xylem.

Water evaporates from the surface of the leaf through the stomata. This type of evaporation from the leaves is called transpiration.

Adaptations of plants to reduce the loss of water:a) Closing of the stomata: At night or at times when it

is very hot, windy or dry.

b) Waxy layer on top of the leaf: Serves as a waterproof layer to minimise evaporation.Eg. Succulents

c) Hairs on the leaf: The hairs trap a layer of moist air against the leaf.

d) Stomata are situated at the bottom of a leaf: This reduces evaporation/transpiration from the leaf.

e) Reducing the surface area of the leaf: To reduce evaporation E.g. Cactus thorns are rolled up leaves. Leaves of plants in warm areas tend to be small while leaves that grow in the shade are big.