Transcript Cells
Cells Cells • The basic unit of life • Microscopic • Organelles – Structures within cells that perform different functions but work together • Two types – Animal cells – Plant cells Animal Cell Plant Cell Organelles in Animal Cells • Cell membrane – – – – Made of proteins and lipids Thin, partially permeable Controls exchange of substances in cell Protects organelles • Cytoplasm – – – – Made of water and dissolved substances Present throughout the cell Provides nutrients, glycogen granules Site of chemical reactions • Nucleus – Controls cell activities – Contains genetic material or DNA in chromosomes Organelles in Animal Cells • Mitochondrion – Pleated membrane to increase surface area – Contains respiratory enzymes – Produces energy through respiration • Vacuole – Fluid-filled membranes – Small, temporary with no fixed shape – Exchange of water, minerals and stores substances including waste • Endoplasmic Reticulum – Several membranes – Make fats and proteins – Contain ribosomes that make proteins Organelles in Plant Cells Only Plant cells contain all the organelles that Animal cells contain in addition to these: • Cell wall – Freely permeable – Made of cellulose – Outside cell membrane – Give shape and protects cell • Chloroplast – Contain green chlorophyll and enzymes – Site of photosynthesis Organelles in Plant Cells Only • Starch grains – Stores carbohydrates • Vacuole – Large, permanent with fixed shape – Contains cell sap – Supports cell when turgid – Stores cell waste • Cytoplasm – A thin layer Specialization • Unicellular organisms made of one cell – Independent of other cells – One cell carries out functions • Multicellular organisms made of many cells – Each cell does a different job – All work together and depend on each other Specialization • Division of Labour – Allows organism to increase in size – Higher productivity and efficiency – Develop special features to carry out specific functions – Different functions can be performed at the same time • Similar or identical cells that perform a specific function are arranged in groups to form tissues Cell Tissues • Several different kinds of tissues are grouped to form an organ Tissue Organ • Organs form larger functional units called systems Organ System • Systems are grouped to form an organism System Organism Bacteria • • • • • Unicellular Microscopic Release toxins Not all harmful Cause diseases – Tuberculosis – Typhoid – Cholera Viruses • Unicellular (smaller than bacteria) • Need other organisms to live • Reproduce only inside living cells – – – – Enter body through openings Attach to then enter host cell Use the host cell to copy itself New viruses destroy and leave the host cell and attack new host cells • All are harmful and cause diseases – – – – Common cold Influenza AIDS Measles Fungi • Very small (yeast) or large (mushrooms) • Do not cause many diseases – Athlelte’s foot – Ringworm Fungi cell Cells of the human body Reactions in Cells 22 Osmosis • Movement of water particles from an area of high water concentration to an area of low water concentration across a selectively permeable membrane. 23 Diffusion • Movement of molecules from a region of high concentration to a low concentration – In gases and liquids – Can occur across thin, permeable membranes • End- products of digestion diffuse from gut into blood • Carbon dioxide and Oxygen diffuse between blood and alveoli • Between blood and cells – Characteristics of surfaces for efficient diffusion • • • • Thin Concentration gradient Moist Large surface area to volume ratio 24 Importance of Diffusion and Osmosis • To bring useful substances to organelles for reactions to take place – Glucose and Oxygen in Respiration • Removal of waste products – Carbon dioxide from respiration, urea – These are secreted out of the cell • Small vessicles transport substances • Hormones are transported this way 25 Active Transport • Transport of molecules across a membrane from a region of lower concentration to a region of higher concentration, using energy. – Allows cells to take up extra substances already present in its cytoplasm .e.g liver and glucose – Allows cell to remove extra substances present in the cytoplasm. 26