Edexcel 9-1 GCSE Biology B1 Summary; Key Concepts in Biology.

Microscopes

Microscopes are used to look at very small objects which are too small to be seen with the naked human eye. Over time, several new models of the microscope have been made to improve the resolution and magnification power of the microscope. The resolution is how clear the enlarged image is, and the magnification is how many times bigger the image is compared to the actual size of the object or specimen. The more common type of microscope to be used in schools is a light microscope, and the most powerful is an electron microscope. Each objective lens has a different magnification and you can change which one you use in an experiment. The coarse and fine adjustment change how close the objective lens is to the stage carrying the slide and how sharp the image is. SI units are used to refer to the length of the specimen (and length of anything in general). Metres (m), millimetres (mm), micrometres (µm), nanometres (nm), and picometres (pm). To get from metres to millimetres, times by 1000, mm to µm, times  by 1000, etc. and to get back, divide by 1000.

Labelled Light Microscope (binary/octet-stream)

Caption: : Labelled light microscope

Animal Cell

Cross Section Of An Animal Cell (binary/octet-stream)

(Lysosomes, centrosomes, ERs, nucleoli, golgi bodies, and vacuoles aren't needed at GSCE.) The membrane-bound nucleus contains DNA. Ribosomes create new proteins.  Cytoplasm is where most of the cells' activity occurs. Mitochondria is where aerobic respiration occurs. The cell membrane controls what enters and leaves the cell and also separates cells.  

Plant Cells

Cross Section Of A Plant Cell (binary/octet-stream)

(Amyloplasts, centrosomes, ERs, golgi bodies, and nuceoli are not needed at GSCE.) The cell wall is an additional 'barrier' made of cellulose and supports and protects the cell. Vacuole stores cell sap and keeps the cell firm and rigid.  Chloroplasts contain chlorophyll, a green pigment, and trap and store energy transferred form the sun to use during photosynthesis. 

Bacterial Cells

Cross Section Of A Bacterial Cell (binary/octet-stream)

Pili are made of protein and allow the cell to attach to other cells. The flagellum is mainly for movement but is also a sensory organelle as it is sensitive to chemicals and temperatures outside the cell. The nucleoid and plasmids store DNA, the nucleoid can also store RNA, proteins, and enzymes.  The capsule protects the cell from outisde threats, such as antibiotics, and can also enhance the ability of the cell to cause disease. 

Specialised Cells

Some cells are specialised in order to complete its respective function correctly or better.  For example, a ciliated epithelial cell is specialised for its purpose in the small intestine.  The black dot is the nucleus. The oblong pink shapes are the mitochondria, aerobic respiration occurs to produce energy so the cells can help to push food through the small intestine.   

Ciliated Epithelial Cell (binary/octet-stream)

Caption: : (Ignore the right diagram)

Gametes

Gametes are specialised cells for sexual reproduction. There are 2 types of gametes, the egg cell (the female gamete) and the sperm cell (the male gamete). Each cell is specialised for its purpose.  The egg cell has a haploid nucleus containing 23 chromosomes of DNA, half of the number of chromosomes in humans. Haploid means the cell contains 1 set of chromosomes, which are tightly wound strands of DNA. The cell membrane/jelly coat protects the cell and allows only one sperm cell to fertilise it. The cytoplasm contains the necessary nutrients and mitochondria for mitosis after fertilisation. 

Egg Cell (binary/octet-stream)

Caption: : Labelled egg cell

A sperm cell's acrosome contains enzymes to break down the coating of the egg cell to fertilise it. The nucleus also contains 23 chromosomes rather than the usual 46 in humans, it is haploid. The collar/mid piece contains many mitochondria to produce as much energy as possible so the cell can move quickly.  The flagellum/tail allows the cell to move. The cell overall also has a very streamlined shape, allowing it to move quickly to the egg cell. 

Sperm Cell (binary/octet-stream)

Enzymes and Nutrition

Enzymes are made of proteins, which are made of amino acids, and are known as biological catalysts, meaning they speed up biological functions. This reduces the need for an increase in body temperatures which would speed up the rate of reaction but requires too much energy.  Every type of enzyme has a specific active site, which is where the substrate (the molecule changed, made or broken down in the reaction) goes because each enzyme is coded for a  different gene. Each type of substrate and its respective type of active site are a complementary fit, they will only fit with each other. This is known as the lock and key theory.  Protein molecules are made of different amino acids, protease breaks them down into amino acids.  Starch/carbohydrate molecules are made of glucose molecules, carbohydrase breaks them down into glucose molecules. Fat/lipid molecules are made up of fatty acids and glucose moelcules, lipase breaks them down into separate fatty acids and glucose molecules. Amylase in found in saliva and breaks down starch into glucose. Catalase is found in cells and breaks down H2O2 in many cell reactions to form water and oxygen. Starch synthase is found in plants and synthesises starch from glucose. DNA polymerase is found in the nucleus and synthesises DNA from it monomers.

Enzyme Activity

EFFECT OF TEMPERATURE When temperatures are too low, there is a low rate of collision between the enzymes and substrates (more heat, more energy, more speed, more collisions). Optimum temperature is when the rate of reaction is at its highest. If the temperature is too hot, the bonds holding the enzyme together break, meaning that the active site changes shape and can no longer fit with the substrate.  EFFECT OF SUBSTRATE CONCENTRATION The rate of reaction will continue to increase as the concentration of the substrate rises until the saturation point is hit. At this point, the amount of substrate matches the number of active sites so the rate of reaction will no longer increase. EFFECT OF pH LEVEL If the pH level is too high or too low, the bonds holding the enzyme together are changed. This means that the active site of teh enzyme no longer fits the substrate shape, therefore the enzyme has denatured and the reaction stops. 

Transporting Substances

DIFFUSION Smells, for example, travel by diffusion. Particles in gases and liquids are constantly moving past each other in random directions, but the particles will always move from an area of high concentration to an area of low concentration, or in adherence with the concentration gradient. This is a passive process and does not require energy. OSMOSIS A membrane that allows some molecules through it and not other is partially permeable. Osmosis is the net movement of water molecules from an area of high water concentration to an area of low water concentration through a partially permeable membrane.  ACTIVE TRANSPORT Cells may need to transport molecules against the concentration gradient, or transport molecules that are too big to diffuse through a membrane. They do this using active transport. This process is carried out by proteins in the cell membrane. This is an active process (says so in the name) and requires energy in the form of ATP.