Cells and tissues Cell structure Photomicrographs Photomicrographs are photos taken of the prepared slides of animals, plants and microorganisms as seen under the microscope. Slides can be prepared in different ways:- i. Cross Section: (CS/TS):- When a very thin section of plant or animal tissue is cut across and stained (methylene blue is blue in color. Iodine is yellow brown in color) and kept on a clean glass slide then covered with a cover slip. ii. Longitudinal section (LS):- When a sample of tissue is cut length wise it is called longitudinal section. To observe a plant cell: We cut sections using razor blade. To observe an animal cell: We soak the organ in melted wax, when wax goes solid we cut the sections, wax is dissolved after making sections. Cell membrane It is the surrounding membrane of the cell. It is made up of the lipids bi-layer and protein pores. It is a semi-permeable membrane which allows certain substance to pass through it. Functions: It allows oxygen, and digested food molecules (amino acid, glucose) to enter. Carbon dioxide and waste product leave the cell. 1
It stops other cell contents from escaping Mitochondria Is a rod-shaped elongated organelle. It contains enzymes which are responsible for aerobic respiration (In aerobic respiration O2 is needed for their electron acceptor) to produce energy from oxidation (is the increase in oxidation state by molecules atoms and ions). The energy produced is stored in form of ATP (Adenosine Tri Phosphate) Ribosome It helps in the synthesis of protein from amino acid. Nucleus It is a rounded structure enclosed in a membrane called nuclear membrane. It contains chromosomes. Functions: It controls the type and quantity of protein or enzymes produced. Nucleus helps in cell division. Nucleus contains DNA which is responsible for passing the genetics from Vacuoles parents to off springs. Animal cells Plant cells Number and size Small and many One and large (gives turgidity to cell by absorbing more water) Components Oil droplets or glycogen Cell sap (mixture of salt, sugar and water) 2
Cytoplasm: Jelly like substance, made up of 90% of water, salts, sugars, lipids and proteins. Under microscope cytoplasm appears to be organized into a complex of membranes and vacuoles. Functions: Different chemical reactions take place in the cytoplasm because enzymes are present. Cytoplasm supports all cell organelles. Cell wall It is made of the carbohydrate cellulose. It is a permeable membrane. Functions: It gives a rigid shape to the cell. It also makes cells turgid and won t burst if they absorbed more water. Plastids I. Chloroplast: Contain green pigment called chlorophyll. It traps sunlight and carry on photosynthesis. II. Chromoplast: These plastids are present in fruits, flowers and colored leaves. They contain pigment of different colors. III. Leucoplast: They are found in rice, wheat and corn in the form of starch. 3
Animal cell Plant cell Cell Wall Absent Present Shape Irregular shape (round) Fixed shape (rectangular) Chloroplast Absent Present Storation of food Glycogen granules Starch granules Cilia Present Rare Plastids Absent Present Cell Division and Specialization Cell Division Animal & Plant cell can divide into two is called Mitosis. Which the daughter cells have same genetic information as parent cells. Out of two cells one may stop dividing (specialized cell) and may continue dividing. Cells which change their shape and structure and adapted to do a particular function and lose their ability to divide are called specialized cells. Division in animal cell 1) Animal cell about to divide. 2) Nucleus divides first. 3) The daughter nuclei separate and cytoplasm pinches off between the nuclei. 4) Two cells are formed one may keep the ability to divide and one may become specialized. Division in plant cell 1) A plant cell about to divide 2) The nucleus divides first. A new cell wall develops and separates the two cells. 3) The cytoplasm adds layers of cellulose on each side of the new cell wall. Vacuoles form in cytoplasm of one cell. 4
4) The vacuoles join up to form one vacuole. This takes in water and makes the cell bigger. The other cell will divide again. Specialized Cells Red Blood cells Have no nucleus instead they have haemoglobin. It combines with oxygen to form HBO They are bicon cave to increase surface area for absorption. Very small and have elastic membranes which squeeze through finest capillaries. They are produced at very high rate because they have very short life (span 120 days) produced in bone marrow. Combine with oxygen to form HBO & transport to all cells and tissues. Muscle cells Store carbohydrate in form of glycogen can be easily changed to glucose. Can respire anaerobically (without oxygen to produce energy for movement.) Have a lot of mitochondria to produce energy for movement. Cytoplasm is modified into contractile filaments which contracts and help in movement. Contraction and relaxation. Ciliated cells They are found in trachea. 5
They have cytoplasmic projections called cilia. Which are in flicking motion. To expel dust particles, bacteria, spores, pollen towards the throat for protection of lungs. There are goblet cells which produce mucus to trap dust particles and bacteria. Protecting lungs from dust particles, bacteria, spores and pollen. White Blood Cells Found in blood stream and they can change their shape and come out of the capillaries to engulf bacteria. Protecting body against foreign harmful bodies. (e.g. Bacteria) Nerve cells They are long so they can carry impulses over a great distance. Have dendrons to receive impulses. It conducts messages in form of electrical impulses from different parts of the body to the brain and from the brain to different parts of the body. Sensory fibres take signals from body parts to the brain. Motor fibres transmit signals from the brain to body parts. Root hair cells 6
They are elongated, thin and plenty to increase surface area for absorption of water by Osmosis.(Movement of water molecules from higher water potential region to low water potential region) Concentrated sap in the vacuole helps it to absorb water from soil. Have many mitochondria to provide energy for active transport. Absorb water and mineral salts from soil. Xylem vessel To transport water and dissolve mineral from the roots to the rest of the plants to carry on photosynthesis. The cell wall is modified into thick lignified walls for support and to be impermeable to water. Xylem is hollow out cytoplasm or cell organelles so the flow of water is not restricted. Xylem is in the form of fine tube trough which water can rise upwards. They are also pits through water can pass out and can be used by cells. Phloem Vessel It transports food in form of sugar from leaves to other parts of plant. Phloem has sieve tubes in which food can pass from leaves other parts of the plants. Companion cells keep the sieve tubes alive by providing them with energy. 7
Tissues and organs The cell is the basic structural and functional unit of all known living organisms. Tissue A collection of similar cells that carry out a specific function. E.g.: Muscle tissue, bone tissues etc Organ A collection of tissues joined in a structural unit to serve a common function. E.g.: Stomach, Heart etc System A group of organs whose functions are closely related. E.g.: Heart and blood vessels make the circulatory system. Organism An organism is any contiguous living system. It can be a plant, animal or any unicellular organism. 8