B8 Photosynthesis

Equation for photosynthesis

>Water + Carbon Dioxide → Glucose + Oxygen

>6H2O + 6CO2 → C6H12O6 + 6O2

What makes photosynthesis an endothermic reaction?

>It needs an input of energy from the environment to break bonds holding carbon dioxide and water together.

>The products of photosynthesis have more energy than reactants.

Plant tissues of a leaf (in order)

>Waxy cuticle

>Upper epidermis

>Paliside mesophyll

>Spongy mesophyll + vascular bundle

>Lower epidermis + stomata (w/ guard cells)

How is a leaf adapted for photosynthesis?

>A plant may produce itself larger leaves which means a larger surface area which can absorb more sunlight

>Chloropast produce a photosynthetic pigment called chlorophyll which absorbs light energy and converts it to chemical energy

>The stomata are located on the lower epidermis which better regulates water loss as there is less sunlight. Water is needed for photosynthesis.

>There is a concentration gradient maintained inside and outside the leaf so it can take in CO2 through the stomata.

>Spongy mesophyll has gaps for air to diffuse so carbon dioxide can be taken to palisade to carry out photosynthesis.

>The lead is thin which allows for a short diffusion distance for carbon dioxide in the leaf.

>Leaves have an abundant network of veins to transport water and mineral ions.

>The stomata is located on the bottom of the leaf which means water transpiration isn’t affected as much by sunlight.

>A waxy cuticle decreases water loss given that it makes it more difficult for water to evaporate from the upper epidermis.

The inverse square law

The intensity of light at different distances from a light source can be described by the inverse square law. This states that the intensity of light is inversely proportional to the square of the distance from the source.

Light intensity ∝ 1/Distance²

or

I ∝ 1/d²

Pondweed experiment instructions

1. Set up a boiling tube containing 45 cm³ of sodium hydrogencarbonate solution (1%). Allow the tube to stand for a few minutes and shake to disperse any air bubbles that might form.

2. Cut a piece of the pondweed. The pondweed should be 8 cm long.

3. Use forcepts to place the pondweed in the boiling tube carefully. Make sure that you don't damage the pondweed, or cause the liquid to overflow.

4. Position the boiling tube so that the pondweed is 10 cm away from the light source. Allow the boiling tube to stand for five minutes. Count the number of bubbles emerging from the cut end of the stems in one minute. Repeat the count five times and record your results.

5. Calculate the average number of bubbles produced per minute. Repeat the experiment at different distances away from the light source.

Pondweed experiment variables

• Independent variable – distance from the light source/light intensity.

• Dependent variable – the number of bubbles produced per minute.

• Control variables – concentration of sodium hydrogencarbonate solution, temperature, using the same piece of Cabomba pondweed each time.

Pondweed experiment risks

Care must be taken when using water near electrical equipment. Ensure that your hands are dry when handling the lamp.

The link between rate of photosynthesis and rage of growth

The faster the rate of photosynthesis, the more glucose and oxygen are produced. These can then be used in respiration to release energy for the plant to use in growth. The glucose can also be converted into cellulose to make cell walls so that more cells can be made.

Plant tissues of a leaf purposes

>Waxy cuticle - Waterproof layer at the top of the leaf which helps to stop the leaf drying out + stops bacteria getting in.

>Upper epidermis - Has cells which do not contains chloroplasts. These cells are there to protect the leaf and focus the sun’s rays onto the cells below.

>Palisade mesophyll - Contains brick shaped cells which are arranged in a row below the upper surface of the leaf. They contains many chloroplasts which contain chlorophyll because they receive maximum amounts of sun and so this is where most of the photosynthesis takes place.

>Spongy mesophyll - contains cells which are rounded in shape and loosely packed together which gaps between called air spaces. They allow gases to diffuse through the leaf and to and from the main photosynthesising cells.

>Lower epidermis - forms a layer on the underside of the leaf which contains holes called stomata through which gasses enter and leave. Those holes can be open or closed depending on special cells around them called guard cells.