Plant Facts

• All organisms including plants and algae need food for respiration, growth and reproduction. This food is represented in the form of glucose, which is made in photosynthesis.

• Plants are producers as they make food using carbon dioxide, water and light.

Limiting Factors

• Photosynthesis has a rate, and requires enzymes.

• Factors effecting photosynthesis include: Temperature, Light, Amount of chlorophyll and carbon dioxide levels.

• The rate of photosynthesis increases when the plant is given higher concentrations of Carbon Dioxide until it reaches a point. Another factor is now preventing the rate of photosynthesis occurring. This is called a limiting factor.

• Light intensity of light to a plant, increasing the rate up to a point. Another factor begins to limit the rate of photosynthesis.

• 1/d² = light intensity

• Light intensity decreases as the distance between the plant and the light source increases.

• As the temperature increases, the rate of photosynthesis increases up until a point.

• Light is a limiting factor when the light intensity is low, but very high light intensity will also cause a slower rate of photosynthesis as well. This can be cause by saturation of the active sites in the enzymes catalysing the reactions or bleaching of chlorophyll.

• Too little carbon dioxide slows down the rate of photosynthesis as well, up to a point. As long as light and carbon dioxide are in plentiful supply, then the limiting factor must be temperature.

• Temperature has to be just perfect in the rate of photosynthesis, as too high can cause the enzymes involved in photosynthesis to denature, and too low can cause the rate to slow down by a lot. The optimum temperature has to be achieved for the enzymes to work at their best.

Glucose uses

• Glucose is used to be converted into amino acids for protein synthesis. Glucose is combined with nitrogen ions from the soil to do this. It is then made into protein (a long chain of amino acids).

• Glucose produces cellulose which strengthens the plant cell walls to be converted into insoluble starch for storage inside cells or special areas.

• Glucose is also used to produce fat or oil for storage as energy store.

• Glucose is turned into starch and stored in the roots, stems and leaves, ready for use when photosynthesis isn’t happening like in the winter. Starch is insoluble which makes it better for storing as glucose would draw in too much water, making the plant swell up.

Features of a leaf

• Most leaves are broad giving them a large surface area for light to fall on.

• Most are thin as well meaning that diffusion distances for the gases are shorter.

• Chlorophyll is contained within chloroplasts to absorb light.

• Leaves have veins which bring in plenty of water in the xylem to the cells of the leaves and remove the products of photosynthesis in the phloem.

• They have air spaces that allow carbon dioxide to get to the cells and oxygen to leave by diffusion.

• They have guard cells which open and close the stomata to regulate gas exchange.

• The leaf has 5 layers- the waxy cuticle, the upper epidermis, the palisade mesophyll, the spongy mesophyll and the lower epidermis.

• The waxy cuticle- To protect the leaf from infection and prevent water loss without blocking out light

• Upper epidermis- To allow more light to reach the palisade cells

• Palisade mesophyll- To absorb more light and increase the rate of photosynthesis

• Spongy mesophyll- Air spaces allow carbon dioxide to diffuse through the leaf

• Xylem is always on the inside and phloem is always on the outside.

• The xylem and the phloem are organised in bundles called veins.

Formulas and reactions

• Photosynthesis is an endothermic reaction as it requires and input of energy from the environment (sun).

• More energy is transferred in breaking bonds (endothermic) rather than forming bonds (exothermic).

• The formula for photosynthesis is= carbon dioxide + water → oxygen + glucose

• Symbol Equation for Photosynthesis- 6CO2 + 6H2O → C6H12O6 +6O2

Hydroponics

• Hydroponics is a method of growing plants by planting them in a water medium. This allows control over all limiting factors, ensuring the speed of growth with perfect balance of nutrients so nothing can stop photosynthesis and no need for soil meaning that no ploughing or prep is needed.

• Hydroponics (adv)- Less staff needed, duration of seed to harvest is shorter, crop larger and cleaner.

• Hydroponics (disadv)- Fuels used to maintain lighting and temperature, expensive monitoring equipment and computers needed to maintain conditions.

Pondweed experiment

• A source of white light is placed at a specific distance from the pondweed. This space is recorded.

• The pondweed (with a cut end and sodium hydrogen carbonate) is left to photosynthesise for a certain amount of time. As it photosynthesises, the bubbles produced will be counted. This is the amount it photosynthesises. The more the bubbles- the higher the amount of photosynthesis.

• The experiment is repeated, each time the distance of the light source being further and further away from the pondweed.

• Independent variable of this experiment= The lamp’s distance from the pondweed

• Control variable of this experiment= The intensity of the light source (the strength of the light)

• Dependent variable of this experiment= bubbles produced per minute