3.2.1 Cell structure

• Cell surface membrane is made mainly of lipids and proteins with carbohydrates which are either attached to one of the two.
• Cell surface membrane regulates the movement of substances in and out of the cell and it also has receptor molecules which allows to respond to molecules.
• Nucleus is a large organelle surrounded by a nuclear envelope, a double membrane which contains many pores.
• The next heaviest organelles (mitochondria) are forced to the bottom and the process continues until all the organelles are separated.
• Nucleus contains chromosomes made from protein bound linear dna and 1 more structure called nucleolus.
• Nucleus controls cell activity controlling transcription of DNA.
• Nuclear pores allow the transfer of substances such as RNA whilst the nucleolus makes ribosomes.
• Mitochondria have a double membrane, the inner is folded to form a cristae.
• Inside mitochondria is a matrix which contains enzymes involved in aerobic respiration.
• Mitochondria is the site of aerobic respiration where ATP is synthesised.
• Chloroplasts are small flattened structures found in plant and algal cells and these contain thylakoid membranes which are folded up to form grana.
• Site of photosynthesis takes place in chloroplasts, some takes place in the grana and others in the stroma.
• Golgi apparatus is a group of fluid filled membrane bounded flattened sacs which often contain vesicles on the edges of the sacs.
• Golgi vesicle is a short fluid filled sac in the cytoplasm surrounded by a membrane and produced by the golgi apparatus.
• Lysosome is a round organelle surrounded by a membrane with a clear inner structure.
• Lysosome contains hydrolytic enzymes used in hydrolysing invading cells or to break down worn out components of the cell.
• Ribosome is a very small organelle and it floats free in the cytoplasm or is attached to the rough endoplasmic reticulum.
• Ribosome is made up of proteins and RNA and it is not surrounded by a membrane, it is the site where protein synthesis occurs.
• Rough endoplasmic reticulum is a system of membranes enclosing a fluid filled space, its surface is covered with ribosomes and it processes and packages proteins made at the ribosomes.
• Smooth endoplasmic reticulum is a system of membranes enclosing a fluid filled space, its surface processes and packages lipids.
• Cell wall is a rigid structure that surrounds the cell in plants, algae and fungi, it supports the cell and prevents it from changing its shape.
• Cell vacuole is a membrane bound organelle found in the cytoplasm of plant cells and it contains the cell sap that contains a wealth of sugar and salts, its surrounding membrane is called the tonoplast.
• Epithelial cells are found in the small intestine and it contains a fold within which are microvilli which increase the surface area needed for absorption such as diffusion of glucose and amino acids, it contains a lot of mitochondria to provide energy for cells.
• Sperm cells contain lots of mitochondria to provide energy to swim to the egg and the head contains many hydrolytic enzymes to break into the egg, its long tails helps to swim to the egg.
• Tissue is a group of specialised cells i.e muscle, nerve, xylem.
• Organ is a group of tissues working together to carry out a particular function i.e heart, lungs, roots, leaves.
• S2 Filtration
• Before fractionation begins, the cells are put in a solution that is:
• It is then filtered to remove complete cells and large pieces of debris.
• Light microscope - They use a beam of light to form an image but due to its longer wavelength it cannot view smaller organelles
• Transmission electron microscope (TEM) - They use electromagnets to focus a beam of electrons which is then transmitted through a specimen
• An isotonic solution is one that has the same water potential as the
• Made up of murein, a glycoprotein.
• Isotonic – to prevent organelles bursting or shrinking as a result of osmotic gain or
• Virus replication - binds to the complementary receptor proteins on the surface of host cells and it injects their dna or rna into the host cell
• Scanning electron microscope (SEM) - They use a beam of electrons in line with the contour of the image to form a highly detailed 3D image
• The denser parts of the specimen absorb more electrons creating a darker image
• Cell fractionation is the process where cells are broken up and the different organelles are separated out
• The specimen has to be thin for it to work and it produces a high quality image.
• S1 Homogenisation