Biology Form 4: Chapter 2: Cell Structure and Cell Organisation

Chapter 2: Cell Structure and Cell Organisation 2.1 Cell Structure and Function 1. Living organisms are made of basic units called cells. 2. Cytoplasm contains structures called organelles. 3. Organelles perform specific functions which enable the cell to function as a unit of life. Cellular components of animal and plant cells.

Cell membrane 1. Made of proteins and phospholipids.

Biology Form 4: Chapter 2: Cell Structure and Cell Organisation

2. Forms a boundary which separates the content of a cell from the outer environment. 3. Plasma membrane is semi permeable and acts as a selective barrier. 4. Function: Regulates the movement of substances into and out of the cytoplasm. Cell wall 1. Rigid outer layer that surround the plasma membrane of plant cells. 2. Composed of cellulose. 3. Permeable to all fluids because it has tiny pores that allow substances to move freely into and out of the cell. 4. Function: a) Gives shape to a plant cell and provides mechanical . b) Protects the plant from rupturing due to the excessive intake of water. Cytoplasm 1. Region between the nucleus and the plasma membrane. 2. Consists of a jelly-like matrix in which organelles are suspended. 3. Contains organic and inorganic substances. 4. Function: a) Acts as a medium for biochemical reactions in the cell. b) Provides substances obtained from the external environment to the organelles. Nucleus 1. Enclosed by a nuclear membrane. 2. Chromatin is contained within the nucleoplasm. 3. Chromosomes carry genetic information which determines the characteristics and functions of a cell. 4. Function: Controls all the activities which take place in the cell. Vacuole 1. Fluid filled sac which is surrounded by tonoplast, a semi-permeable membrane. 2. The fluid contained in a vacuole is called cell sap. 3. Function: Acts as a storage place in a cell. 4. The cell sap contains water, organic acids, sugars, amino acids, mineral salts, waste susbstances, pigments and metabolic by-products. 5. The cell sap in a vacuole s herbaceous plants so that they do not wilt easily. Mitochondria 1. Small spherical or cylindrical-shaped organelle. 2. Involved in cellular respiration. Ribosomes 1. Compact spherical organelles found attached to the surface of rough endoplasmic reticulum or suspended freely in the cytoplasm. 2. Consists of two subunits, one small and one large, each of which comprises a type of ribonucleic acid (RNA) and protein. 3. Function: Site of synthesis of proteins. 4. Use information carried by the chromosomes to make these proteins. Endoplasmic reticulum 1. Rough endoplasmic reticulum - ribosomes attached to the surface.

Biology Form 4: Chapter 2: Cell Structure and Cell Organisation

- transports proteins made by the ribosomes. 2. Smooth endoplasmic reticulum - Site of important metabolic reactions, including synthesis of lipids and detoxification of drugs and poisons. Golgi apparatus 1. Function: Processing, Packaging and transporting centre of carbohydrates, proteins, phospholipids and glycoproteins. Transport vesicles 1. Carry products such as proteins from the endoplasmic reticulum and fuse with membrane of the Golgi apparatus and empty their contents into the membranous space. 2. Carry products from Golgi Apparatus to other parts of the cell or to the plasma membrane. Lysosomes 1. Membrane bound sacs that contain hydrolytic enzymes. 2. Hydrolytic enzyme digest or breaks down complex organic molecules such as proteins, lipids, polysaccharides and nucleic acids. 3. Eliminate worn out mitochondria and other damaged organelles. 4. Fuse with food vacuoles and dispense enzymes into these vacuoles to digest the contents of the vacuoles. This releases nutrients needed by the organisms. 5. Digests bacteria by breaking down the bacterial wall. Centrioles 1. Function: Form spindle fibres during cell division in animal cells. Chloroplasts 1. Contain the green pigment chlorophyll. 2. Chlorophyll traps sunlight and converts light energy into chemical energy during photosynthesis. The density of organelles in specific cells 1. Pancreatic cells which synthesise and secrete enzymes and hormones contain a high density of rough endoplasmic reticulum. 2. Sperm cells which require large amounts of energy to propel towards the uterus and Fallopian tube during fertilization contain a high density of mitochondria. 3. Flight muscle cells in insects and birds contract and relax to enable movement and flight contain a high density of mitochondria too.