Essay about biology revison gcse

Submitted By frankielaw
Words: 2565
Pages: 11

B2.1
Animal cells:-
In the organelle, the nucleus controls the cells activates and it is surrounded by the cytoplasm. It contains the DNA and genetic material that provides the instructions for synthesising the chemicals the cell needs like enzymes.
Mitochondria use glucose in reparation to release energy for the cell
Ribosomes build up proteins from smaller, simpler compounds called amino acids.
Plant cells:-
Cell wall is made of the carbohydrate cellulose
Chloroplasts contain chlorophyll, the chemical which absorbs the sunlight that is used for photosynthesis. Light energy is converted into chemical energy in the form of glucose
Vacuole is filled with cell sap that contains sugars, salts and water
Palisade mesophyll cells-found in the liar and paced with chloroplasts
Xylem vessels- made up of empty dead cells, long tubes of cell wall, transport water from the roots up through the steam to the leaves. Does not rot due to chemicals from the cell wall
Bacteria and yeast:-
Bacteria are unicellular organisms. It consists of cytoplasm surrounded by a membrane and an outer cell wall. The cell wall is not made from cellulose. No nucleus but only ribosomes. Cytoplasm contains a loop of DNA that contains the cells genes.
Each yeast cell has a nucleus, cytoplasm, mitochondria, a vacuole and cell membrane and a cell wall. 10x bigger than bacteria
Diffusion:-
The net movement of a substance through a partially permeable membrane on a high to low concentration gradient
Organ systems:-
Zygote-the cell formed when two gametes fuse
This cell divides repeatedly to form identical cells which then differentiate into a specific function
Tissues are made up of similar specialised cells that have the same structure and function
Cells in glandular tissus produce and release particular chemicals such as enzymes and hormones
Epidermal tissues cover the plant and the mesophyll tissue carries out photosynthesis in the leaf and the xylem and phloem tissues transport substances around the plant
Groups of tissues are called organs. You stomach is an organ; the inner wall contains glandular tissue that produces digestive juices, epithelial tissue cover the outside and inside of the stomach and has three types of muscle.
B2.2
Photosynthesis:-
Carbon dioxide+ water=glucose+ oxygen
Glucose has energy stored in its bonds which can be used for growth
Chloroplasts are found in palisade cells in upper layer of the leaf. The chlorophyll absorbs light energy which is used to convert carbon dioxide and water into glucose
Conversions of glucose:-
The plant converts excess glucose into starch to be used later on, such as when it is cold
Useful as it is insoluble and doesn’t react easily with other chemicals in the cytoplasm.
Some plants store energy as fats called lipids. They provide more glucose for respiration than carbohydrates
Cells need proteins to form enzymes and cell membranes. Plant cells synthesise proteins from glucose and nitrate. Soluble nitrates can be absorbed through cell membranes from soil or water
Greenhouses and polytunnels:-
Enhancing light; greenhouses provide extra light through lamps. However plants grow too tall and therefore shade smaller trees for receiving it. Only works with small densely packed plants. Also expensive electricity bills
Enhancing co2; levels in a greenhouse are increased by burning fuels such as propane or adding the gas through a PVC tubing.
Controlling temperature; greenhouses must be kept between 25 degrees and 30 degrees in winter. They are heated by boilers and radiators. Summer it gets to hot so vents are opened in the roof and blinds are lowered
Too hot and the enzymes denature causing reactions to not take place. Too cold and the enzymes don’t have enough energy to carry out reactions
B2.4
Proteins:-
Proteins make up hair, nails and skin
Protein molecules, in the form of haemoglobin, carry oxygen in your blood and help if you are injured by clotting blood
All proteins contain the same four elements: carbon,…