OBE Biology Notes Form 4 & 5 2024 PDF

Biology Notes Form 4 & 5 2024 OUTCOMES BASED EDUCATION SYLLABI  MODULE BIOSL 1: EXPLORE CONTINUITY AND DIVERSITY OF LIFE Learning Outcome: BIOSL 1.1 – Analyse cell processes and maintenance Performance Criteria: PC - 1.1.1 to 1.1.11 MICROSCOPY (PC 1.1.1 – 1.1.2)  Mi...

Biology Notes Form 4 & 5 2024 OUTCOMES BASED EDUCATION SYLLABI  MODULE BIOSL 1: EXPLORE CONTINUITY AND DIVERSITY OF LIFE Learning Outcome: BIOSL 1.1 – Analyse cell processes and maintenance Performance Criteria: PC - 1.1.1 to 1.1.11 MICROSCOPY (PC 1.1.1 – 1.1.2)  Microscopes and microbiology  linking advance  The microscope is the microbiologist’s most basic tool.  Microscopes use lenses to magnify object’s images.  There are many types of microscopes (look at the next slide) but the most common include two types: ◦ Light microscopes (5 types) ◦ Electron microscope (2 types)  Light microscope used to examine cells at relatively low magnifications and electron microscope used to lock at cells and cell structure at very high magnification. Principles of Light Microscope  Compound light microscope uses visible light to illuminate cells.  Many different types of light microscopy:  1-Brightfield  2-Darkfield  3-Phase-contrast  4-Differential interference contrast (DIC)  5-Fluorescence Bright-field microscope  Specimens are visualized because of differences in contrast (density) between specimen and surroundings.  Contrast differences arise because cells absorb or scatter light to varying degrees. Two sets of lenses form the image.  Objective lens and ocular lens (compound)  Total magnification = objective magnification  ocular magnification  Maximum magnification is ~2,000 Some Principles of Light Microscope  Magnification is not the limiting factor in the ability of seeing small things but also, we need a good resolution which is the ability to distinguish two adjacent objects.  Magnification can be increased without limit, but resolution cannot because it is the function of physical properties of light.  Light microscopy limits resolution is about 0.2µm, electron microscope resolution is greater than of light microscope.  Resolution: the ability to distinguish two adjacent objects as separate and distinct  Resolution is determined by the wavelength of light used and numerical aperture of lens. Try Labelling Phase – Contrast and Dark – Field Microscopy  Two forms of light microscopy improve image without using staining.  Phase –contrast microscopy is based on the principle that cells differ in refractive index from their surroundings.  Phase – contrast microscopy resulting a dark image on light background.  The dark-fielded microscopy is a light microscope in which the light reaches the specimen from the sides only. Thus, the specimens appear light on a dark background.  The dark-fielded microscopy used in observed microbial motility. Fluorescence Microscopy  Used to visualize specimens that fluoresce – emit light of one colour following absorption of light of another colour.  Cells fluoresce either:  Contain naturally fluorescent substances such as chlorophyll.  Because cells have satin with fluorescent dye.  DAPI (4`,6-diamidino-2-phenylindole) is widely used fluorescent dye staining cell`s DNA. Electron Microscopy  Electron microscopes use electrons instead of photons (visible light) to image cells and structures.  Electromagnets function as lenses in EM, whole system operates in a vacuum.  EM are fitted with cameras to allow a photograph to be taken.  Two types of electron microscopes:  Transmission electron microscopes (TEM) (need thin section), negative stain  Scanning electron microscopes (SEM) Coat with heavy metal  Transmission electron microscopy is used to examine cells and cell structure at very high magnification and resolution, even enabling one to view structures at the molecular level.  This is because the wavelength of electrons is much shorter than the wavelength of visible light and wavelength affects resolution.  Unlike visible light, electron beams cannot penetrate very well. So, special techniques of thin sectioning are needed to prepare specimens before observing them.  To obtain sufficient contrast, the preparation are treated with stains such as osmic acid, permanganate, uranium, lanthanum; because these substances are composed of atoms of high atomic weight, they scatter electrons well and thus improve contrast.  Scanning electron microscopy used to observed external features of an organisms or cell.  No need for thin sections.  The specimen is coated with a thin film of a heavy metal such as gold.  An electron beam then scans back and forth across the specimens. Electrons scattered from the metal coating are collected and activate a viewing screen to produce an image. PROKARYOTIC & EUKARYOTIC CELLS (PC 1.1.3) All cells fall into one of the two major classifications of either prokaryotic or eukaryotic.  Prokaryotic cells were here first and for billions of years were the only form of life on Earth. All prokaryotic organisms are unicellular.  Eukaryotic cells appeared on earth long after prokaryotic cells, but they are much more advanced. Eukaryotic organisms unlike prokaryotic can be unicellular or multicellular. Characteristics of Prokaryotes  Prokaryotes are the simplest type of cell.  Oldest type of cell appeared about four billion years ago.  Prokaryotes are the largest group of organisms.  Prokaryotes unicellular organisms that are found in all environments.  Prokaryotes do not have a nuclear membrane. Their circular shaped genetic material dispersed throughout cytoplasm.  Prokaryotes do not have membrane-bound organelles.  Prokaryotes have a simple internal structure.  Prokaryotes are smaller in size when compared to Eukaryotes. Characteristics of Eukaryotes  Eukaryotic cells appeared approximately one billion years ago.  Eukaryotes are generally more advanced than prokaryotes.  Nuclear membrane surrounds linear genetic material (DNA).  Unlike prokaryotes, eukaryotes have several different parts.  Prokaryote’s organelles have coverings known as membranes.  Eukaryotes have a complex internal structure.  Eukaryotes are larger than prokaryotes in size. Differences Tabulated Prokaryotic Cell Eukaryotic Cell Organelles lack a membrane. Organelles covered by a membrane. Ribosomes are the only organelles. Multiple organelles including ribosomes. Genetic material floats in the cytoplasm (DNA Membrane covered Genetic material. and RNA) Circular DNA Linear DNA Unicellular May be multicellular or unicellular. Cells are smaller in size. Cells are larger in size. It has larger number of organisms. It has smaller number of organisms. Appeared 4 billion years ago. Appeared 1 billion years ago. Similarities of Prokaryotes & Eukaryotes  Both types of cells have cell membranes (outer covering of the cell)  Both types of cells have ribosomes  Both types of cells have DNA  Both types of cells have a liquid environment known as the cytoplasm CELL COMPONENTS (PC 1.1.4 – 1.1.6) What is a cell? There are many definitions of a cell; some of them include the following;  A cell is the smallest basic unit of life.  It is a basic unit from which all living organisms are made.  It the basic structure and function in living organisms  A cell is the smallest part of a living thing that can exist independently. Cells are invisible to the naked eye; they cannot be seen with a naked eye. For one to see a cell there is need to use a microscope. The study of cells by microscopy is known as Cytology. Some organisms such as Bacteria and many Protoctists are made from just one cell (amoeba, Euglena etc) and they are known as unicellular organisms. Plants and animals are made from many different cells, and they are known as multi-cellular. ANIMAL CELL  PLANT CELL Parts of the cell and their functions 1. Cell Wall: it is a non-living organelle made from Cellulose/fibre and other compounds. It provides structural support (pressure of cell contents leads to turgidity) and protects against damage caused by osmotic intake of water. The cell wall is freely permeable to water and dissolved substances. It also gives the cell its shape. 2. Cell surface membrane: the organelle that surrounds the cytoplasm. It is selectively permeable membrane which controls the entry of dissolved Hydrophilic region substances (such as food, Oxygen and water), exit of waste products (such as Carbon dioxide, urea etc) Hydrophobic region and also prevents the entry of harmful substances. Hydrophilic region Phospholipid Proteins (b) Structure of the plasma membrane 3. Cytoplasm: contains water, dissolved substances such as amino acids, fats and granules of starch which are contained in some particles found in it. It holds and supports various parts of the cell (organelle). It has also been forum to contain enzymes and there are some chemical reactions taking place in the cell that keep the cell alive by providing energy for the cell. 4. Nucleus: it is found in the cytoplasm. It is a very important organelle. It contains DNA (Deoxy-Ribonucleic Nucleus Nucleolus Acid) which makes up genes on the chromosomes. Chromatin Nuclear envelope: Chromosomes become visible during cell division. This Inner membrane Outer membrane carries coded instructions for controlling the activities and Nuclear pore characteristic of a cell. the nucleus also controls cell division and this makes it impossible for cell without a nucleus to reproduce. It also controls the type and quantity of enzymes produced by the cytoplasm and by doing so regulating the chemical changes that takes place in the cell. The nucleus together with the cytoplasm and cell membrane are known as Protoplasm. 5. Vacuoles: they are permanent in plants and temporary vacuoles in animals. Permanent vacuoles in plants contain Cell Sap (a watery solution containing dissolved salts, sugars and sometimes pigments). This cell sap is responsible for providing the turgor pressure, may store ions and molecules. In animals, temporary vacuoles are small become available only when needed for a certain task (e.g in phagocytes)  6. Chloroplasts: a green pigment organelle only available in plant cells. It contains chlorophyll pigment (for light absorption) and enzymes necessary for the production of starch (or glucose) by Photosynthesis. 7. Mitochondria: are spherical and rod like or elongated organelle which are present in both plants and animal cells. This is a site where respiration occurs with the help of food substances that enter the cell. 8. Ribosomes: these are very small organelles consisting of a small and large subunit; these are sites for protein synthesis. 9. Golgi apparatus: This is a stack of flattened, membrane-bounded sacs. They are responsible for storage and transportation of lipids and special proteins. **10. Lysosomes: it a simple spherical sac bounded by single membrane and containing digestive enzymes. It has many functions, it breakdown structures or molecules (autophagy) in simple terms it cleans the cell by digesting all the dead or dirt organelles in organisms. The Differences between Plant and Animal Cells: FEATURE PLANT CELL ANIMAL CELL CELL WALL Present: made of cellulose Absent CHLOROPLAST Present Absent VACUOLE Present Absent FOOD STORE: Carbohydrates Starch, Glucose Glycogen FOOD STORE: Protein Can Store protein Cannot store protein FOOD STORE: Fats/lipids Oils Fats SHAPE Regular (due to cell wall) Irregular shape SIZE Large Small Define the following Terms & give Examples: a. Tissue ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… Examples: ……………………………….. ………………………………. ………………………………. b. Organ ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… Examples: ……………………………….. ………………………………. ………………………………. c. System ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… Examples: ……………………………….. ………………………………. ………………………………. d. Organism ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… Examples: ……………………………….. ………………………………. ………………………………. CELL DIVISION (PC 1.1.7 – 1.1.8) MITOSIS Mitosis produces two daughter cells that are identical to the parent cell. If the parent cell is haploid (N), then the daughter cells will be haploid. If the parent cell is diploid, the daughter cells will also be diploid. It involves the somatic/body cells. There is a dormant/resting stage known as Interphase, Mitosis consists of four stages;  Prophase,  Metaphase,  Anaphase and  Telophase Stages of Mitosis: INTERPHASE It is a dormant stage; chromosomes are not visible. DNA duplicate (copy itself). New cell parts (organelles) are formed. If present, the Centrioles multiply. The cell builds up energy store to carry out the mitosis process. Chromosomes are not visible because they are uncoiled. Stages of Mitosis: PROPHASE Chromosomes become visible and they contain DNA molecules. As prophase continues, the chromosomes coil, become shorter and fatter. The chromosomes separate and form chromatids and they are joined together by the centromeres. Spindle Fibres start forming in the cytoplasm, with an equator and a pair of Centrioles at each pole. The nuclear membrane starts to breakdown. The chromosomes coil. The nuclear membrane disintegrates. The spindle apparatus forms. Stages of Mitosis: METAPHASE  In early metaphase, chromosomes are arranged at the equator (middle) of the spindle fibre. with the chromatids of each chromosome oriented/adjusted towards opposite poles.  Chromatids are attached to the spindle fibres by their centromeres.  The centromeres then divide and may begin to move apart in opposite directions, carrying the chromatids towards the poles of the spindle. Stages of Mitosis: ANAPHASE The chromatids separate, the number of chromosomes doubles. The drawing shows a cell with 16 chromosomes. Each chromosome has 1 chromatid for a total of 16 chromatids. Stages of Mitosis: TELOPHASE Chromatids reach the poles of the cell, uncoil, and become thinner, losing the ability to visible. (Chromosomes reform by an uncoiling, they become thinner and disappear). Spindle fibres disintegrates. Nucleic membrane develops under a set of chromatids. At this point in animal cells, the cytoplasm between two nuclei constricts (Become tight or as if tight) and the two cells are formed. This stage is followed by distribution of organelles to form 2 potential daughter cells followed by development of loosely cells referred to as cytokinesis. IMPORTANCE OF MITOSIS ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… SUMMARY OF MITOSIS  MEIOSIS Meiosis is a reductive cell division which reduces chromosomes to half and produces sex/germ cells. It is a cell division that produces reproductive cells in sexually reproducing organisms; the nucleus divides into four nuclei each containing half the chromosome number (leading to gametes in animals and spores in plants). All body cells contain a constant number of chromosomes e.g. human beings contain 46 chromosomes. Meiosis leaves the chromosomes in a haploid state (n) and it results in 23 chromosomes. It will be after fertilization that the chromosomes will become 46 again (with 23 pairs from the ovum and the sperm). To have four daughter cells, there is need for two cell division in meiosis at the end of the first cell division there is going to be 2 daughter cells which will divide to form two other daughter cells the stages are similar to mitosis. Meiosis produces daughter cells that have one half the number of chromosomes as the parent cell. Stages of First Meiosis: MEIOSIS – PROPHASE I This is the longest stage of meiosis and involves the following; The nucleolus breaks down along with the nucleus membrane. Chromosomes shorten and become thick. Unlike in mitosis, the homologous (similar chromosomes) pairs of chromosomes lie together. As prophase continues, the chromosomes coil around each other. Crossing over occurs. Stages of First Meiosis: MEIOSIS – METAPHASE I Paired chromosomes move to the equator of the spindle formed as in mitosis. They become arranged, with the centromeres of homologous pairs pointing towards opposite poles. The random alignment pattern is called independent assortment. For example, a cell with 2N = 6 chromosomes could have any of the alignment patterns shown at the left Stages of First Meiosis: MEIOSIS – ANAPHASE I  Homologous chromosomes (each consisting of two chromatids joined at the centromeres) move apart towards opposite poles of the spindle. Stages of First Meiosis: MEIOSIS – TELOPHASE I  (this stage is absent in some species) Chromosomes reach the poles and the cell constricts forming two new daughter cells as in mitosis.  The division has halved the chromosomes of the original  Nuclear membranes may re-form and a short resting space follows but occasionally the cell enters the metaphase 2 stage. SUMMARY OF MEIOSIS I Stages of Second Meiosis: MEIOSIS – METAPHASE II  a new spindle forms in each new cell and two chromosomes line up at the equator. Stages of Second Meiosis: MEIOSIS – ANAPHASE II  Chromatids of the chromosomes in each new cell separate (as in mitosis) Stages of Second Meiosis: MEIOSIS – TELOPHASE II  Four new cells form, each with half the chromosomes compared to the original cell. END OF MEIOSIS  SUMMARY OF MEIOSIS II The Differences between MITOSIS and MEIOSIS: MITOSIS MEIOSIS It is a duplicative cell division. It is a reductive cell division. Forms somatic/body cells Forms gametes/sex cells. Forms 2 diploid (2n) cells. Forms haploid (n) gametes (sex cells). Responsible for the growth of an individual Responsible for reproduction. Completed after one division. Completed after two divisions. No pairing of homologous chromosomes. Homologous chromosomes pair in prophase 1. Two cells formed Four cells formed. CELL SPECIALISATION (PC 1.1.9) Animal Cells Specialization In animals, the first type of cells in the developing embryo are stem cells. These are unspecialized cells that go on to form all the different cell types in the adult. Erythrocytes (Red Blood Cells) Structure: Red blood cells (RBCs) are small & flexible so that they can squeeze through tiny blood vessels therefore taking blood to all parts of the body. They are also bi-concave which gives them a large surface area which speeds up the exchange of oxygen from the cell. The cytoplasm of the cell has a red pigment known as haemoglobin which enables it to carry Oxygen around the body. Function: Transport oxygen from the lungs to all parts of the body of an organism. Neurone (Nerve Cell) Structure: Cells have long extension to transport impulses over longer distances. Function: transports messages to the brain or spinal cord and from the parts in the form electric impulses for interpretation for an action to be taken. Muscle Cell Structure: Long & have numerous protein fibres in the cytoplasm. (Fibre helps to shorten the cell when there is energy). Can contract & relax in order to move parts. Function: It moves bones in different directions (contract / relax to help move structures). Sperm Cell Structure: Has streamlined head to enable it to move towards ovum with less friction. Has a tail to help it swim towards the ovum. Function: Fuse with ovum to from a zygote White Blood Cell Produced in the white bone marrow (especially the phagocytes), lymph nodes of the lymphatic system (especially the lymphocytes) and sometimes in the spleen. Have an irregular shape and their cytoplasm can flow and help them to move through blood capillaries. They are fewer than the red blood cells. They are divided into 2 main groups: Granulocytes (phagocytes) and Agranulocytes (lymphocytes) White Blood Cell (Phagocytes) Structure: They have: granules/particles in their cytoplasm a lobed nucleus which enables them to change shape to engulf pathogens by phagocytosis and digest it and the cell disintegrate/break up. An open wound has the remains of dead cells and digested bacteria and form pus which later removed to facilitate healing. Function: Defend the body against infections through phagocytosis. White Blood Cell (Lymphocytes) Structure: They have no granules in their cytoplasm, but have a large bean shaped/spherical nucleus e.g. lymphocytes. They produce pathogen specific antibodies (which are protein in nature). The antibodies are released into the circulatory system and are transported to the  infected area where they destroy harmful pathogens like bacteria. Function: Antibodies attack germs in the following ways:  makes them stuck together,  destroy cell wall and toxins and  dissolves/disintegrates them. defend the body against infections through use of antibodies. Plant Cells Specialization  Unlike animals, many plant cells retain the ability to differentiate and specialize throughout their life.  These cells are found in tissues called meristems. Root Hair Cell Structure: Large number of mitochondria to generate energy needed from active transport of ions. Has a finger-like projection that enables to penetrate tightly packed soil particles. Have Large concentrated sap vacuole which ensures water uptake through osmosis. Function: Absorb water from the soil. Absorb mineral ions (salts) from the soil. Anchor the plants firmly to the ground. Xylem Cell Structure: Has dead hollow tube without cytoplasm to allow flow of water. Walls are lignified (coated with lignin) to withstand water pressure. Cylindrical cells are attached end to end form a xylem vessel. Function: Transport water & dissolved minerals from the roots to top part of a plant. Supports the plant against mechanical damage. Phloem Cell Structure: 2 types of phloem cells - companion cells and sieve tube members. Sieve tube members - tubes that material moves through. Companion cells assist sieve tube members. Function: Transport manufactured food from the photosynthetic organs to other parts of the plant where they are used or stored. The transport of food substances in the phloem is known as translocation. Palisade Cell Structure: Has lots of chloroplasts to produce chlorophyll which traps sunlight energy for the process. Elongated so that they can pack tightly. Located close to the upper epidermis to receive more sunlight. Function: To make sugar (starch) through photosynthesis. Guard Cell Structure: Crescent shaped Always paired to form a stomata. Are able to change shape to close / open depending on whether its day or night. Function: To regulate the opening & closing of stomata MOVEMENT OF SUBSTANCES (PC 1.1.10 – 1.1.11) There are three processes that are involved in the movement of substances in & out of the cells: Diffusion Osmosis Active transport DIFFUSION Definition: It is the random movement of particles from their region of their higher concentration to their region lower concentration down a concentration gradient until they are evenly distributed.  N.B. Diffusion occurs in all states of matter. a) Diffusion in gases  The spread of perfume particles (or air freshener) from the nozzle of the spray can fill up the room occurs through diffusion. b) Diffusion in liquids  The spread of potassium permanganate from the bottom of a beaker to the top is by diffusion. Factors Affecting Diffusion Changes in temperature  An increase in temperature increases the kinetic energy of particles; hence particles will move faster leading to an increase in the rate of diffusion. Particle size  Small particles dissolve faster because they are less dense & have a large surface area, hence can diffuse rapidly from one end to the other. Concentration gradient  This is the difference in the number of particles between two adjacent areas. Particles move faster when the difference in the number of particles is large. The rate of diffusion diminishes as the concentration gradient reduces. OSMOSIS Definition: It is the random movement of water molecules from their region of higher concentration to their region of lower concentration along the concentration gradient through a partially / selectively permeable membrane. Similarities between Osmosis & Diffusion  Particles are moving down the concentration gradient.  Both processes are passive, no energy is expended (used). Differences between Osmosis & Diffusion OSMOSIS DIFFUSION Occurs mainly in liquids (only water molecules Occurs in all states of matter (any particle is are moved). moved). Materials are moved across a barrier (a partially Does not require a barrier (partially membrane). permeable membrane required). Osmosis & Tonicity What is Tonicity?  It is the ability of a solution to cause a cell to gain or lose water.  It has a great impact on cells without walls. Isotonic Solution If a solution is isotonic  The concentration of solutes is the same as it is inside the cell.  There will be NO NET movement of WATER. Hypertonic Solution If a solution is Hypertonic  The concentration of solutes is greater than it is inside the cell.  The cell will lose water. Hypotonic Solution If a solution is Hypertonic  The concentration of solutes is less than it is inside the cell.  The cell will gain water. Osmosis in Animal Cells Summarized Osmosis in Plant Cells Summarized ACTIVE TRANSPORT Definition: This is the movement of materials from their region of low concentration to their region of high concentration against the concentration gradient using energy from respiration. Unlike osmosis & diffusion: It occurs against the concentration gradient. It requires energy. Only mineral ions are moved.  MODULE BIOSL 1: EXPLORE CONTINUITY AND DIVERSITY OF LIFE Learning Outcome: BIOSL 1.2 – Apply knowledge of classification of living organisms to group them into kingdoms. Performance Criteria: PC - 1.2.1 to 1.2.4 KINGDOMS OF LIVING THINGS (PC 1.2.1) Diversity refers to variety of living things. Organisms are grouped according to common characteristics. Grouping of organisms according to characteristics is called CLASSIFICATION or TAXONOMY (the study of classification). The main characteristics used to group living things are: Feeding Structure Reproduction The Five Major Kingdoms of Living Things MONERA e.g. Bacteria PROTISTA e.g. Protozoa (animal like) and Protophyta (plant like) FUNGI e.g. mushroom, toadstools etc. ANIMALS e.g. vertebrates and invertebrates PLANTS e.g. flowering and non-flowering. THE VIRUSES Viruses do not feed, respire or reproduce on their own as such it is debatable whether they are living or non-living organisms. They are just in their own class. They are on the border line between living and non-living because they can only survive and reproduce inside the living cells. Viruses differ from living cells in at least three ways: Their simple, acellular organization, The absence of both DNA and RNA in the same virion, Their inability to reproduce independently of cells and carry out cell division as prokaryotes and eukaryotes do. Examples: HIV, Corona virus, Bacteriophages (used to fight off some bacterial diseases to kill bacteria), herpes, influenza and polio viruses. Three main classes animal viruses, bacterial viruses (bacteriophages), and plant viruses. VIRUSES: Structure Smaller than bacteria. Have a capsid (outer coat). Surrounds DNA/RNA A virus can have either DNA or RNA but never both !! No organelles Various shaped   Helical viruses resemble  The capsid of most  The capsid of viruses is long rods that may be polyhedral viruses is in covered by an envelope. rigid or flexible. e.g. the shape of a regular e.g. Corona virus tobacco mosaic virus polyhedron e.g. adenovirus, poliovirus VIRUSES: Nutrition Viruses do not feed. If they were to feed, we would say:  They are parasitic (need a host cell for metabolism) e.g., feeding and reproduction.  Also, heterotrophic VIRUSES: Reproduction Reproduce asexually. They penetrate a living cell by first attaching to the cell membrane of the host cell & then either. Injects its DNA / RNA into the cell’s cytoplasm. OR  The whole virus may be taken in; after which it gets uncoated in the host cell. The genetic material replicates & multiplies inside the host cell; it takes over the cell’s activities. Eventually the cell bursts & releases the new virus which can infect other cells. Invasion Process Importance of Viruses Human viruses include; common cold, poliomyelitis, measles, mumps, chickenpox, rubella, influenza & HIV. How viruses are useful to man; They are used to make vaccines for hepatitis. May be used to deliver recombinant DNA in genetic engineering. How viruses are harmful to man; They cause diseases such as HIV / AIDS, influenza etc. THE BACTERIA (Kingdom Monera) e.g Spirillium, E. coli, Agtobacteria, Bacillus, Streptococcus BACTERIA: Structure Vary in shape i.e., they are grouped based on their shape e.g. cocci (spherical), streptococci (chain shaped), rod shaped e.g. bacillus. They are unicellular (single celled). Do not have a true nucleus (has a prokaryotic cell structure). They are very small. Have a thick external cell membrane made up of a slim protein coat (capsule) especially in disease causing bacteria. DNA material is found naked in the cytoplasm (no membrane). Flagella (tail like structures) present in some species. Do not have a vacuole. No chloroplasts May have chlorophyll but not chloroplast. BACTERIA: Nutrition  Some are saprophytic i.e. feed on dead and decayed matter.  Some are parasitic i.e. they obtain food by living in other organisms. (heterotrophy) = saprophytic + parasite.  Others are autotrophic i.e. they are either phototrophic or chemoautotrophic e.g. nitrogen fixing bacteria. BACTERIA: Reproduction  Some bacteria produce sexually by conjugation (fragments of genetic material are exchanged).  They can also produce asexually through binary fission. It takes place every 20 minutes). THE FUNGAE Fungi (Kingdom Fungae) e.g. yeast, mushroom, toadstools, penicillin. There are around 80 000 known species of fungi. Ranges from the unicellular yeast to the large (multicellular) toadstools, puffballs, mushrooms etc, which occupy a very wide range of habitats, both aquatic & terrestrial. FUNGAE: Structure  No chlorophyll  Cell is rigid.  Cannot move.  Have a unique body structure consisting of a mass of fine, tuber like branching threads-like filaments called Hyphae which make up the mycellin.  Have cell walls made of Chitin, not cellulose as in plants.  Simplest ones are unicellular.  Has a nucleus  Vacuole is large.  Contains organelles.  The protoplasm may be continuous or interrupted at intervals by cross-walls called sectors. FUNGAE: Nutrition  They are heterotrophic because of lack of chlorophyll.  Some fungi are saprophytes.  Parasitic  They are mutualistic/symbiotic.  The main storage polysaccharide is glycogen. FUNGAE: Reproduction  Reproduce asexually by sporulation (use of spores). The spores produced are carried by wind or rain when the sporangium opens.  They can also reproduce asexually through budding.  Can also reproduce sexually through the hyphae. THE PROTISTA Three categories of Protists: Animal-like (Protozoa) Plant-like (Protophyta) Fungi-like PROTISTA: Structure Unicellular (single celled) Flagella present in some species. Have organelles. Other have cilia (tiny hairs) e.g. paramecium Others have false legs (pseudopodia) for movement and capturing food. They are mobile and some are animal like PROTISTA: Nutrition  Some are heterotrophic (feed on other animals e.g. paramecium  Feed on microscopic plants and animals by moving towards them using pseudopodia.  Some are parasitic e.g. plasmodium  Some are autotrophic e.g. Euglena PROTISTA: Reproduction  Produce asexually by binary fission or multiple fission.  Paramecium can undergo sexual reproduction by conjugation. THE GREEN ALGAE  Chlamydomonas – unicellular motile algae  Spirogyra – filamentous algae  Alva (seed weed) – a thylloid marine algae GREEN ALGAE: Structure Filamentous alga with chloroplasts and they are green. Some are unicellular and others are multicellular. Some are simple plants without true roots, stems, leaves and vascular bundle. Found on the surface of stagnant or still water. Store carbohydrates as starch They have cellulose cell wall. Some have pigment spot (red eye spot) to detect light sand move towards it. E.g. Chlamydomonas GREEN ALGAE: Nutrition Filamentous alga with chloroplasts and they are green. Some are unicellular and others are multicellular. Some are simple plants without true roots, stems, leaves and vascular bundle. Found on the surface of stagnant or still water. Nutrients are absorbed through the cell wall together with water. They are photosynthetic because they are green, and they are known to be autotrophic. GREEN ALGAE: Reproduction Sexual Reproduction  This involves the combination of genetic material from two individuals of the same species as in spirogyras & Chlamydomonas. Asexual Reproduction  Fragmentation – this occurs in filamentous algae such as spirogyra. The filament breaks in a controlled manner somewhere along its length to form two filaments. ANIMALIA: Arthropods Arthropods (Kingdom Animalia: Phyllum Arthropoda): Insects, spiders, snails, crabs e.t.c Common features: exoskeleton segmented body jointed legs ANIMALIA - ARTHROPODS: Structure Have jointed legs and appendages (body parts) adapted for swimming, walking and grasping. They are bilaterally symmetrical, segmented, triploblastic bodies. Have a complete digestive system with mouth and anus. Have a well-developed gas exchange system, including the tracheal system of insects. Body covered with exoskeleton made from chitin and proteins. They are invertebrates. Most have compound eyes and a marked head region. They have a reduced coelom with the large haemocoel which acts as a hydrostatic skeleton. Some have antennae. They can undergo ecdysis. ANIMALIA - ARTHROPODS: Nutrition  They are heterotrophic.  Have distinguished mouthparts for feeding on different food.  Most are predators e.g. spiders, dragon flies, lady birds, ants.  Some have poison glands for protection against predators and to kill prey e.g. scorpions. ANIMALIA - ARTHROPODS: Reproduction  Sexes are separate and therefore produce sexually by fertilization of gametes then lay eggs.  The eggs undergo metamorphosis (complete and incomplete metamorphosis.  For growth ecdysis (molting) occurs (loss of old exoskeleton and growth of new one). INSECTS ARACHNIDS MYRIAPODS CRUSTACEANS ANIMALIA: Chordata Vertebrates (Kingdom Animalia; Phyllum Chordata) e.g. fish, birds, amphibians, reptiles, mammals ANIMALIA - CHORDATA: Structure Have a vertebral column/backbone. Have an internal skeleton (endoskeleton) Genetically different. Have a hollow dorsal nerve tube. Have a spinal cord ending in the brain. Have pancreas and liver. Have a well-developed closed blood system. A tail behind the anus. Have lungs or gills for breathing. ANIMALIA - CHORDATA: Nutrition  They are heterotrophic.  Have distinguished mouth parts for feeding on a specific diet.  Digestive system is complete (runs from mouth to anus).  Some are: herbivores (plant eaters), carnivores (flesh eating), predators (chase and catch prey), omnivores (eat both plants and animal flesh), scavengers (eat what has already been killed). ANIMALIA - CHORDATA: Reproduction  Produce sexually by fertilization of gametes.  Some vertebrates e.g. fish, amphibians, reptile undergo external fertilization.  Have well developed sexual organs. PLANTAE: Angiosperms Angiosperms e.g. grass, weeds, maize, rice (those that can bear flowers) PLANTAE - ANGIOSPERMS: Structure Basic unit is a cell wall. Chlorophyll present Have distinctive roots, stems, leaves and vascular tissues. PLANTAE - ANGIOSPERMS: Nutrition They are autotrophic (produce their own food through photosynthesis). PLANTAE - ANGIOSPERMS: Reproduction  Fertilization of gametes occurs in the flower.  Seeds are produced and protected by the fruits.  Can produce asexually; grafting, budding, cutting, layering. PLANTAE - GYMNOSPERMS: Structure Have an advanced vascular system which carries water from the roots to the needle like leaves. Can photosynthesize in cold conditions. Produce resin that prevents freezing of the cytoplasm. Do not shed leaves during winter (they are evergreen). PLANTAE - GYMNOSPERMS: Nutrition They are autotrophic (produce their own food through photosynthesis) PLANTAE - GYMNOSPERMS: Reproduction  Reproductive structures occur in cone.  The seeds which are formed as a result of fertilization are not enclosed in fruits.  The seeds are naked.  Produce diploid zygote (sporophyte), the embryo with its small food supply is released as a small, winged seed. DICHOTOMOUS KEY (PC 1.2.2 – 1.2.4) Scientists have identified and classified over one and a half million species of animals, plants, fungi and other organisms on the earth. Species are identified by scientists all over the world by a uniform classification and naming system. What is Classification?  Classification: putting things into orderly groups based on similar characteristics Early classification was done by Aristotle, he grouped everything into simple groups such as animals or plants. He then grouped animals according to if they had blood or didn’t have blood, and if they had live young or laid eggs, and so on…  Taxonomy: the science of describing, naming, and classifying organisms.  Binomial Nomenclature:  Developed by Carolus Linnaeus  Swedish Biologist 1700’s  Two-name system  Genus and species named using Latin or Greek words. Rules used to write scientific names:  An organism’s genus is always written first; the organism’s species is always written second.  The genus is Capitalized; the species is written in lower case.  Scientific names of organisms are always italicized or underlined. e.g. Ursus maritimus The modern system of classification has 8 levels:  Domain  Kingdom  Phylum  Class  Order  Family  Genus  Species Definition:  A system for identifying organisms that offers two, and only two alternatives at each choice.  It is a process of identifying an organism with a series of steps, each containing two questions. The answers lead you along a path until the organism is identified. NB: Scientists Need to Speak the Same Language! Nomenclature: How scientists name living things by sorting into groups. Taxonomic Key (Dichotomous Key):  Paired statements that describe the physical characteristics of different organisms.  Dichotomous (dīˈkätəməs) means divided in two parts.  When you use a dichotomous key, you follow a path. Each choice along the path has only two questions. The answer is always YES or NO. Example of a Key What is this crazy bug???? Basic Rules for Constructing Dichotomous Keys All parts of the key should be dichotomous. Never use trichotomies. Always give contrasting, alternative characteristics in each couplet. Use clear-cut opposites. Taxonomic names should never be used in the characteristic description. Use characteristics that are convenient and obvious features of the organism. Each step involves making choices between 2 characteristics. The characteristics are grouped 1a and 1b, 2a and 2b and so forth. Another Example of a Key Suppose you have four insects a ladybug, a housefly, a dragonfly and a grasshopper. After studying the insects, what characteristics could you use to start separating the four insects?? wing covering body shape where the wings point towards To begin the key, you could start separating the four insects based on wing covering - "wings covered by exoskeleton" vs. "wings not covered by exoskeleton." The first step in the key will be organized the following way: CHARACTERISTIC 1 a. wings covered by an exoskeleton 1 b. wings not covered by an exoskeleton Next, the statements need to lead the observer to the next step to narrow the identification further: CHARACTERISTIC GO TO/ IDENTIFY 1 a. wings covered by an exoskeleton ……………………….go to step 2 1 b. wings not covered by an exoskeleton …………………..go to step 3 Step 2 needs to consist of a pair of statements that will allow for the identification of the ladybug and the grasshopper: 2 a. body has a round shape ………………………………….ladybug 2 b. body has an elongated shape …………………………….grasshopper Step 3 needs to consist of a pair of statements that will allow for the identification of the housefly and dragonfly: 3 a. wings point out from the side of the body ………………dragonfly 3 b. wings point to the posterior of the body ………………...housefly NB: Notice that there were four organisms to be identified and it only took three steps. There should be one less step than the total number of organisms to be identified in your dichotomous key. When using a key, keep the following in mind: Always read both choices, even if the first seems to be the logical one at first. Be sure you understand the meaning of the terms involved. Do Not Guess. Since living things are always somewhat variable, do not base your conclusion on a single observation. Study several specimens to be sure your specimen is typical. If the choice is not clear, for whatever reason, try both divisions. If you end up with two possible answers, read descriptions of the two choices to help you decide. Having arrived at an answer in a key, do not accept this as absolutely reliable. Check a description of the organism to see if it agrees with the unknown specimen. If not, an error has been Made somewhere, either in the key or in its use. The ultimate check of identifications is a comparison of the unknown with an authentically named "Type Specimen". Dichotomous Key for Students: GIVE IT A TRY!!!  MODULE BIOSL 1: EXPLORE CONTINUITY AND DIVERSITY OF LIFE Learning Outcome: BIOSL 1.3 – Evaluate the role of reproduction in continuity of life. Performance Criteria: PC - 1.3.1 to 1.3.15 PLANT REPRODUCTION (PC 1.3.1 – 1.3.8) Asexual Reproduction in Plants: Definition: A process of producing Genetically Identical Offspring (CLONES) from one parent. Asexual Reproduction in other organisms: Budding Binary fission Vegetative Propagation Also known as vegetative propagation in plants. Vegetative propagation: NATURAL OR ARTIFICIAL NATURAL Vegetative Propagation Tubers Rhizomes Runners Suckers Bulbs Tubers: Tubers are underground swollen stems or roots. Can later become individuals. stores food over the winter and provides a new plant with food until it can make its own. Food made by the new plant is sent to make new tubers. Thereby reproducing itself. Examples: potato, artichoke, yam, cassava, water chestnut, arrowroot. Rhizomes: Underground stems which develop roots & shoots develop at the nodes. Examples: spear grass, ginger Runners (Stolon): Runners are side shoots (stems) which grow along (above) the ground out from the parent plant. Roots & shoots develop at the nodes. Examples: spider plant (Anthericum), strawberry (Fragaria x ananassa). Bulbs: Specialized underground organs with fleshy stems & thick leaves. Vegetative organ @the centre of the bulb. Examples: onions, lilies, daffodils, beetroot, reddish. Suckers: New growths that occur at the base of the parent plant. Main stem develops buds. These buds develop into a new plant. Examples: bananas Artificial Vegetative Propagation Methods used to cultivate plants asexually: Grafting Layering Cuttings Grafting: A cut stem of one plant (with good flower or fruit growth) (the graft/scion) Is firmly attached to the rootstock of another plant (which has a strong, established root system) (the stock). Examples: citrus plants, apple trees, tea plants, etc. Cuttings: Cuttings are small pieces of stem with some leaves attached, the new plant grows from this. They can be placed in moist soil or water (and sometimes dipped in rooting powder). Examples: roses Advantages of Asexual Reproduction (mitosis)/Commercial Aspects It is the simplest & shortest way of reproduction. The chances of offspring survival are greatly enhanced. There is no danger of gametes getting destroyed before fusion. Ideal for preservation of good characteristics within the population. Possible to produce a large number of offspring within a short time. Disadvantages of Asexual Reproduction Defects and diseases from parents are easily passed to offspring. Inhibits evolutionary change because of no variation. Differences between Asexual & Sexual Reproduction Sexual Reproduction in Plants: A flower is a leafy shoot containing the sexual organs of a flowering plant. It is adapted for sexual reproduction. It is a modified terminal bud typically composed of four sets of modified leaves. Flower Structure: Sepals Protects the flower during the bud stage. Petals Attracts insect pollinators by colour and scent. Anthers produce and release pollen grains. Filament positions the anther for effective pickup of pollen by the pollinating agent. Stigma collects the pollen from the pollinating agent. Style positions the stigma for pollen collection. Ovaries site of fertilisation, protects the developing seeds, aids in seed dispersal. Insect Pollinated Flower Petals large & brightly coloured to attract insects. Stigma located inside the flower where the insects have to brush past it. Anthers inside the flower where the insects have to brush past them. Stigma usually small & sticky so that pollen grains can attach from insect body. Flower often strongly scented. Large sticky or spiky pollen grains which stick to insects. Wind Pollinated Flower Petals small or absent, if present, not brightly coloured. Stigma exposed to catch pollen grains blowing in the wind. Anthers exposed outside the flower so that wind can easily blow the pollen grains away. Stigma large & feathery to catch pollen grains blowing in the wind. Flowers have no scent. Light & smooth pollen that can be blown in the wind. Pollination Definition: the transfer of pollen grains from the male part of the plant (anther of stamen) to the female part of the plant (stigma). Types of Pollination There are two types (cross and self): a) Cross pollination - where pollen from anther of a flower from one plant is transferred to the stigma of a flower of another plant of the same species. It results in more variation.  b) Self-pollination - where pollen from anther lands onto the stigma of the same flower OR where pollen from anther of one flower is transferred to the stigma of anther flower within the same plant. NB: Cross pollination is favoured by plants. It is used in the production of crops with combination of desirable traits. It brings about variation in plants, prevents spread of genetically spread diseases and produces healthier offspring. Agents of Pollination The means that moves the pollen grains from the anther to the stigma. Agents of pollination include: wind; insects; birds; water & rodents. Pollen Tube Formation & Fertilization After pollination, pollen grains germinate to form pollen tube. Petals and other parts that were necessary for pollination dry out and fall. The carpel remains attached to the calyx. It is worth noting that plants secrets different combinations of sugars at the stigma. These sugars are used to identify members of the same species in order for the development of the pollen tube. If a pollen grain of a totally different plant species falls of the stigma, no pollen tube develops. The pollen tube grows down the style to the ovary. Pollen tube transports the pollen nucleus (haploid) to the ovule (haploid). The pollen nucleus and the ovule carry half the total number of chromosomes that is haploid in genetical terms. Enzymes at the tip of tube digest tissues on its way, allowing it to grow towards the ovary.  NB: ovule becomes seed. ovule wall becomes seed coat or testa. ovary becomes fruit. stigma and the style weathers and dry up. Seed & Fruit Dispersal This is spread of seeds & fruits some distance away from the parent plant. Dispersal allows seeds to spread out to colonise new areas so that the new plants do not compete with parent plant for light, water and mineral salts. means of seeds & fruits are: animals wind water self-dispersal Seeds and Fruits Dispersed by WIND Wind dispersed seeds such as sycamore & dandelion: are light so that they can easily be blown by wind. have wing –like outgrowth or feathery hair projections which increase the surface area so that the seeds can ‘float’ in air for some time, so they are carried over long distance from the parent plant. Seeds and Fruits Dispersed by ANIMALS Animal dispersed seeds includes: tomato & burr grass. Tomato fruits: they are fleshy (succulent), brightly coloured & scented to attract animals. Have tough seed coat to protect the seeds from being digested in the animals' gut. Burr grass: Are covered with stiff, hooked spines which catch onto the animals’ fur to be carried long distance before dropping off. Advantages of Seed Dispersal There is less competition, with parent plant & among seedlings for same resources such as; light, water, nutrients & space. Dispersal allows plants to colonise new areas since plants are stationary i.e. don’t move from place to place. Seed Structure & Germination Testa protects the embryo from physical damage & attack from pathogens. Micropyle a hole in the testa that allow water & oxygen to enter into the seed. Cotyledons stores nutrients (starch, protein & lipids) required during germination. Plumule grows into shoot after germination. Radicle grows into root after germination.  EXTERNAL SEED STRUCTURE INTERNAL SEED STRUCTURE Germination & the Conditions Seed germination: is the process in which a plant emerges from a seed & begins grow. Conditions needed for seeds germination are: Suitable temperature: for enzymes to work effectively. Oxygen: for aerobic respiration to provide energy to growing embryo. Water: for chemical reactions to occur in solution, dissolve nutrients for transportation, activate enzymes & soak testa. HUMAN REPRODUCTION (PC 1.3.9 – 1.3.15) Male Reproductive System Testes: they produce sperms & the hormone testosterone. Scrotum: a special sac outside the abdominal cavity containing testes. At this position testes are kept at a temperature slightly below the body temperature. This is the best temperature for sperm production. Sperm ducts: carry sperms from the testes to the urethra. Prostate gland: it secretes a fluid that activates & feed sperms. Seminal vesicle: it secretes a fluid that activates aids in sperm mobility. Urethra: it carries urine & semen (fluid containing sperms) out of the male’s body. Epididymis: A coiled tube that stores sperms Penis: It is used to deposit sperms into the female’s vagina during sexual intercourse. SIDE VIEW  FRONT VIEW Female Reproductive System Ovaries: they produce ova (eggs) and the hormones oestrogen & progesterone. Oviducts: the tube through which the ova pass when released from the ovary. It is also a region where fertilization occurs. Uterus: the region where the embryo is implanted after fertilization in the oviduct. Cervix: A ring of muscle closing the lower end of the uterus where it joins the vagina. It dilates / widens during childbirth. Vagina: it accommodates (receives) the penis during sexual intercourse. It is where sperms are deposited from the male and also serves as a birth canal. SIDE VIEW FRONT VIEW Differences between Male & Female Gametes MALE GAMETE (SPERM) FEMALE GAMETE (OVUM) Smaller in size (diameter of sperm head Larger in size (diameter of 0.05mm) is 0.01mm) Has no food store Has a food store Has a tail which helps it to swim towards Does not move by itself (move by the the egg help of cilia within the oviducts) Produced in large numbers Produced in small numbers Life span is 2 – 3 days (i.e., sperms might Has a life span of 24hours after being be able to fertilize an ovum within 2 – 3 produced days) Fertilization Once deposited into the vagina sperms swim up through the cervix & uterus to the oviducts where they meet with an ovum. More than 500 million sperms are released from a single ejaculation, but only one sperm is needed to fertilize the ovum. During fertilization the tail of the sperm remains outside as the head travels through the cytoplasm to deliver the nucleus Fertilization is defined as the fusion of the sperm nucleus with the egg nucleus to from a zygote. Egg membrane changes form in order to prevent further entry of other sperms. Zygote divides through mitosis forming an embryo as it travels down into uterus - Implantation. Pregnancy A number of changes occur in uterus to allow for a successful growth of the embryo. These include formation of: Placenta: a region that allows for the exchange of substances between mother & foetus. Umbilical cord: made of umbilical artery which carries deoxygenated blood & waste from foetus & the umbilical vein bringing oxygenated blood & nutrients from mother to the foetus. Amnion: a membrane that surrounds the foetus & produces amniotic fluids Amniotic fluid: a watery fluid that protects the foetus from external shock. Placenta & the Umbilical Cord Amniotic Sac & Amniotic Fluid The amnion (also called amniotic sac) is a thin membrane covering the embryo & has a protective function. The sac is filled with a fluid known as amniotic fluid which supports the embryo & protect it from mechanical shock. As the embryo increases in size the amniotic sac also expands to accommodate it. Identical Twins Twins resulting from the separation of one fertilized egg to form two complete individuals. These individuals may share the placenta & amnion. They also have the same sex & closely resemble each other in every respect. Fraternal Twins Twins resulting from two different ova fertilized by two different sperms. Each embryo will have its own placenta & amnion. It is possible that they may be of the same or different sexes & may not resemble each other. Stages of Birth A. Labour:  gradual dilation of the cervix to a diameter allowing safe passage of the head into the vagina.  Oxytocin hormone is secreted by the pituitary stimulating the contraction of the uterine muscles.  The amniotic sac ruptures and the amniotic fluid escapes by way of the vagina. B. Birth:  passage of the baby from the uterus through the cervix and along the vagina to the outside.  The umbilical cord is clamped closed near to the baby and cut on the far side of the clamp. C. Afterbirth:  the expulsion of the placenta from the mother. THE MENSTRUAL CYCLE Four major hormones in the menstrual cycle: Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) Oestrogen Progesterone This cycle ranges from 24 to 35 days, and is commonly 28 days. Phases of the menstrual cycle 1. Menstruation Phase 2. Repair Phase (safe period phase) 3. Receptive Phase 4. Pre-menstrual Phase Menstruation Phase (Day 1 to 5) Corpus luteum disintegrates. Levels of Progesterone drops. Uterine lining is shed. Blood, mucus & uterus cells are lost through the vagina. Low levels of progesterone & oestrogen stimulate the release of FSH from the Pituitary gland. Repair Phase (safe period-Day 6 - 13) FSH stimulates formation of the Primary Follicle. Follicle matures to Graafian follicle. Maturing follicle secretes Oestrogen. Oestrogen inhibits FSH-preventing maturation of other follicles. Oestrogen stimulates the repair of the uterine lining. Receptive Phase (Day 14) The lining of the uterus and its blood vessels are now well developed. The surge of LH stimulates ovulation - release of the egg cell from the mature Graafian follicle at the ovary's surface (Ovulatory phase). The egg cell is drawn into the Fallopian tube. If fertilization occurred, the embryo can be implanted in its lining. At this point any unprotected sexual activity will lead to pregnancy. Pre-menstrual Phase (Day 15 – 28) A corpus luteum develops from the remains of the Graafian follicle. After ovulation, the follicle develops into Corpus luteum, which secretes the female hormone Progesterone. The corpus luteum secretes progesterone and oestrogen stimulating the final maturation of the uterine lining (Luteal phase). If implantation does not take place by day 26, the corpus luteum disintegrates. The lining of the uterus degenerates as the progesterone levels drop unless implantation has occurred. This phase is usually characterized with some contraction of the uterus leading to period pains. Rapid decline in the levels of progesterone and oestrogen due to the degeneration of the corpus luteum. NB: High levels of these hormones also inhibit FSH and LH secretion from the pituitary. Birth Control Methods Barrier Methods Condoms (male & female) Diaphragm (the cap) Intra-Uterine Device (IUD) Chemical/Hormonal Methods Spermicidal Creams The Pill Norplant Injection Surgical Methods Vasectomy Tubal ligation Natural Methods Rhythm method (safe period) Withdrawal Other Methods Douching Abstinence Sexually Transmitted Infections (STIs) SYPHILIS Causes: Bacteria Transmission: Unprotected Sex From mother to child (during pregnancy) Signs & Symptoms First stage – painless sores appear on genitals or site of infection, which can heal after 4 – 8 weeks. Second stage – skin rash, lymph nodes enlarge, headache, aches & pains in the bones. Third stage – brain & heart damage which occur within 10 years of original infection. During birth a baby’s eyes may become infected as it passes through the cervix & vagina. Treatment Antibiotics e.g. Penicillin Control Abstinence Condom use Be faithful to your partner. GONORRHOEA Causes: Bacteria Transmission: Unprotected Sex From mother to child (during pregnancy) From mother to child (during delivery) Signs & Symptoms In males Yellowish smelly discharge from the penis Painful urination May lead to the blockage of the urethra and sperm ducts leading to sterility. In females Painful urination Yellowish & smelly discharge from the vagina. Oviducts may become blocked resulting in sterility. Bacteria may invade the baby’s eyes at birth & cause blindness. May not show any signs at first stage. Treatment Antibiotics e.g. Penicillin Control Abstinence Condom use Be faithful to your partner. ACQUIRED IMMUNE DEFICIENCY SYNDROME (AIDS) Cause Human Immunodeficiency Virus (HIV) Transmission Unprotected sexual intercourse with an infected person Sharing unsterilized sharp objects (razors, needles) with an infected person Blood transfusion using infected blood Mother-to-child during pregnancy, birth & breast feeding Symptoms Chronic fever, severe diarrhea lasting for months, pneumonia, brain infections, tuberculosis, loss of weight. Effect Insanity and death Treatment none or no cure Control ARV therapy Prevention Avoid sharing of sharp objects and sterilizing them before use etc. NB: HIV attacks the immune system making it weak. The body then fails to defend itself against infections and opportunistic diseases attack. Weakening of immune system eventually leads to AIDS. HIV – person has no virus in the blood. The person has to keep the status by living positively. HIV+ person has the virus in the body but does not show symptoms of the disease. The patient can live longer, more than 10 years, if he/she lives positively by abstaining, using a condom every time and eating well, balanced diet. AIDS patient shows symptoms of the disease. Implications of STIs 1. Loss of skilled manpower 2. Loss of bread winners (increase of poverty) 3. Increase in orphans. CANCERS Prostate Cancer (causes, signs & symptoms, Treatment) ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. Cervical Cancer (causes, signs & symptoms, Treatment) ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. Ovarian Cancer (causes, signs & symptoms, Treatment) ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. Breast Cancer (causes, signs & symptoms, Treatment) ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….  MODULE BIOSL 1: EXPLORE CONTINUITY AND DIVERSITY OF LIFE Learning Outcome: BIOSL 1.4 – Apply knowledge of heredity to solve problems. Performance Criteria: PC - 1.4.1 to 1.4.10 HEREDITY & GENETICS (PC 1.4.1 – 1.4.10) Terminologies: Inheritance: Attributes acquired via biological heredity from the parents. Genetics: The branch of biology that studies heredity and variation in organisms. Meiosis: Cell division that produces reproductive cells. The nucleus divides into four nuclei each containing half the chromosome number (leading to gametes in animals and spores in plants). Mitosis: Cell division in which the nucleus divides into nuclei containing the same number of chromosomes. Mutation: Any event that changes genetic structure; any alteration in the inherited nucleic acid sequence of the genotype of an organism. Centrioles: One of two small cylindrical cell organelles composes of 9 triplet microtubules; form the asters during mitosis. Crossing over: The breaking during meiosis of one maternal and one paternal chromosome, the exchange of corresponding sections of DNA, and the rejoining of the chromosomes. This process can result in an exchange of alleles between chromosomes. Compare recombination. Autosome: A chromosome not involved in sex determination. The diploid human genome consists of 46 chromosomes, 22 pairs of autosomes, and 1 pair of sex chromosomes (the X and Y chromosomes).  Diploid: A full set of genetic material, consisting of paired chromosomes one chromosome from each parental set. Most animal cells except the gametes have a diploid set of chromosomes. The diploid human genome has 46 chromosomes. Compare haploid. Haploid: A single set of chromosomes (half the full set of genetic material), present in the egg and sperm cells of animals and in the egg and pollen cells of plants. Human beings have 23 chromosomes in their reproductive cells. Compare diploid. DNA (deoxyribonucleic acid): The molecule that encodes genetic information. DNA is a double- stranded molecule held together by weak bonds between base pairs of nucleotides. The four nucleotides in DNA contain the bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Gamete: Mature male or female reproductive cell (sperm or ovum) with a haploid set of chromosomes (23 for humans). Gene: The fundamental physical and functional unit of heredity. A gene is an ordered sequence of nucleotides located in a particular position on a particular chromosome that encodes a specific functional product. Locus (pl. loci): The position on a chromosome of a gene or other chromosome marker; also, the DNA at that position. The use of locus is sometimes restricted to mean regions of DNA that are expressed. See gene expression. Somatic cells: Any cell in the body except gametes and their precursors. Nucleotide: A subunit of DNA or RNA consisting of a nitrogenous base (Adenine, Guanine, Thymine, or Cytosine in DNA; adenine, guanine, uracil, or cytosine in RNA), a phosphate molecule, and a sugar molecule (deoxyribose in DNA and ribose in RNA). Thousands of nucleotides are linked to form a DNA or RNA molecule. Ribonucleic acid (RNA): A chemical found in the nucleus and cytoplasm of cells; it plays an important role in protein synthesis and other chemical activities of the cell. The structure of RNA is similar to that of DNA. There are several classes of RNA molecules, including messenger RNA, transfer RNA, ribosomal RNA, and other small RNAs, each serving a different purpose. ALLELES Alternative forms of a genetic locus; a single allele for each locus is inherited separately from each parent (e.g., at a locus for eye color the allele might result in blue or brown eyes). Each gene can exist in a number of forms e.g. TT, Tt, tt. Different pairs of the same gene are called alleles. They are found at the same locus (position) but on different chromosomes of the homologous pair. Alleles also control alternate characteristics e.g. Tallness and shortness. In the case of eye colour for humans one allele may be for the blue eyes and another might be for brown eyes. CHROMOSOMES The self- replicating genetic structures of cells containing the cellular DNA. In prokaryotes, chromosomal DNA is circular, and the entire genome is carried on one chromosome. Eukaryotic genomes consist of a number of chromosomes whose DNA is associated with different kinds of proteins. Chromosomes are thin, thread-like structures which are found in the nucleus of the cells, they carry genes. In ordinary resting cells, chromosomes cannot be seen, but when the cell is about to divide, they can be seen because at this stage they become shorter and fatter making them show up distinctly. Homologous & Heterozygous Chromosomes Chromosomes are present in homologous pairs. They are identical in length and gene number. One chromosome of the pair comes from the male parent and the other from the female parent. Heterozygosity: The presence of different alleles at one or more loci on homologous chromosomes. Homologous chromosomes: A pair of chromosomes containing the same linear gene sequences, each derived from one parent. HOMOZYGOUS - Possessing a pair of identical genes controlling the same characteristics: will breed true for the characteristics. (True for dominant alleles). E.g. TT – Homozygous dominant (homozygote) tt – Homozygous recessive HETEROZYGOUS - Carrying a pair of contrasting genes for any heritable characteristic: will not breed true for the characteristics. Both alleles are present at a locus. E.g. Tt – Heterozygous Genotype & Phenotype Genotype: genetic make-up or composition of an organism. Phenotype: the outward manifestation of the genotype (physical appearance). Gene: made up of two alleles e.g.  BB – Homozygous dominant  Bb – Heterozygous  bb – Homozygous recessive Incomplete, Complete & Co-dominance Monohybrid Crossing Crossing: sexual reproduction process in genetic terms. A cross involves the fusion of nuclei of gametes. Monohybrid crossing: Passing of characteristics from parents to offspring. F1 generation: offspring produced after breeding of one generation. F2 generation: offspring produced after the interbreeding of F1 generation. More Monohybrid Crosses More Crossing More Crossing More Crossing BACK/TEST CROSS The way to discover an unknown genotype is by carrying out a further cross known as the Test Cross. The test cross is used to determine the genotype of a dominant phenotype. It always involves crossing of the unknown genotype to the homozygous recessive. This is the genotype of one of the parents in the standard monohybrid cross and that is why it is also known as Back Cross. INCOMPLETE DOMINANCE Strictly applies to a case where the effect of a recessive allele is NOT completely masked by the dominant allele. E.g. Sickle cell Anaemia: It affects haemoglobin in red blood cells. It causes the red blood cells to distort when the blood is deoxygenated. This is an allele in humans which if inherited in the homozygous recessive form gives rise to a condition called sickle cell anaemia. Incomplete Dominance Example: a) Normal allele: HbA HbA (Do not have sickle cell anaemia - Dominant) ACTIVITY: Perform a genetic cross s s b) A sufferer: Hb Hb of parents who are (Severe anaemia - Homozygous recessive) Heterozygous to determine phenotypes of offspring. c) Sickle-celI trait/carrier: HbA Hbs (Mild symptoms of anaemia - Heterozygous) NB: Dominant Allele is not completely dominant over a Recessive Allele Incomplete Dominance Crosses More Incomplete Dominance Crossing CO-DOMINANCE If both genes in a pair produce their effects in an individual, the alleles are called co- dominant. In some cases, a single characteristic such as blood group in humans is controlled by one gene which has 3 alleles. Co-dominance: Blood Groups They can be represented as follows:  A: for blood group A (presence of A – antigen)  B: for blood group B (presence of B – antigen)  O: for blood group O (no antigen present) Alleles A and B are dominant to allele O. Alleles A and B are co-dominant. There are four phenotypic blood groups. A, B, AB, and O. These blood groups are controlled by a single gene which is normally represented by the letter I. The four blood group phenotypes have the following genotype. Co-dominance Crossing Complete Dominance This is a condition where there are two types of genes, a dominant and a recessive one. The dominant gene will completely show overpower the presence of the recessive gene. Example: Albinism Results from a mutation in the genes Albinos are unable to produce the dark pigment melanin, which controls skin colouration, so that the colour fails to develop. The Albinism allele is recessive to the pigment producing allele. Complete Dominance Crossing Pedigrees for Monohybrid Crosses A Pedigree is a record of the ancestry of an individual. A pedigree in the form of a chart can be used to illustrate the transmission of a heritable condition in a family. MUTATION Mutation is a change or alteration in form or qualities. Genetics definitions of mutations: In genetics it is defined as any event that changes genetic structure, any alteration in the inherited nucleic acid sequence of the genotype of an organism. It can also be defined as genetic mechanisms which change the structure of genes. It is sudden change in the genotype of a cell. A Mutation occurs when a DNA gene is damaged or changed in such a way as to alter the genetic message carried by that gene. Any offspring produced by an individual with a mutation, showing the new characteristics is known as a mutant. Mutations are the basis of discontinuous variation. Mutation can be good and sometimes can be deleterious or dangerous. Mutation can be induced by factors known as mutagens/mutagenic agents e.g. X-ray, gamma rays, ultra violet rays, cosmic rays (from the outer space) and chemicals such as gas. Mutations can lead to cancer. Types of Mutation There are two main types: Gene and Chromosome mutation. Mutation usually occurs when the eggs and sperms are being formed during meiosis. Gene Mutation They are important in generating evolutionary changes and they affect the nucleotide (the basic structural unit of nucleic acids (DNA or RNA)) structure of the gene. It is usually a result of a chemical change in an individual gene. The change may be very small, but it may have a severe effect on an individual. E.g., sickle cell anaemia and cystic fibrosis, PKU (Phenylketonuria), albinism. Chromosome Mutation This involves a major change in one or more chromosomes. An individual may lack a particular chromosome or have an extra chromosome e.g., Down syndrome is caused by the presence of an extra chromosome in the somatic/body cells. The resulting offspring has 47 chromosomes instead of the normal 46 human chromosomes. The extra chromosome comes from the mother or the father. During meiosis an extra chromosome may result when one of the duplicated chromosomes does not separate. The extra chromosome upsets he usually orderly development of the body and the brain. Chromosomal mutations are usually lethal and sometimes useful because the involve chromosomes being moved from the locations or even changing during independent assortment or crossing over. Types of Chromosome Mutation Mutations at chromosome level can be a result of the following; Inversion of Genes This is where the order of a particular order of genes are reversed as seen below: Translocation of Genes This is where information from one of two homologous chromosomes breaks and binds to the other. Usually, this sort of mutation is lethal. Deletion of a Gene As the name implies, genes of a chromosome are permanently lost as they become unattached to the centromeres and are lost forever. Duplication of Genes In this mutation, the mutant’s genes are displayed twice on the same chromosome due to duplication of these genes. This can prove to be an advantageous mutation as no genetic information is lost or altered and new genes are gained. Factors Leading to Mutations (Mutagens) Chemical Mutagens: change the sequence of bases in a DNA gene in a number of ways. Mimic/copy the correct nucleotide bases in a DNA molecule but fail to base pair correctly during DNA replication. Remove parts of the nucleotide (such as the amino group on adenine), again causing improper base pairing during DNA replication. Add hydrocarbon groups to various nucleotides, also causing incorrect base pairing during DNA replication. Radiation High energy radiation from a radioactive material or from X-rays is absorbed by the atoms in water molecules surrounding the DNA. This energy is transferred to the electrons which then fly away from the atom. Left behind is a free radical, which is a highly dangerous and highly reactive molecule that attacks the DNA molecule and alters it in many ways. Radiation can also cause double strand breaks in the DNA molecule, which the cell's repair mechanisms cannot put right. Sunlight contains ultraviolet radiation (the component that causes a suntan) which, when absorbed by the DNA causes a cross link to form between certain adjacent bases. In most normal cases the cells can repair this damage, but unrepaired dimers of this sort cause the replicating system to skip over the mistake leaving a gap, which is supposed to be filled in later. Unprotected exposure to UV radiation by the human skin can cause serious damage and may lead to skin cancer and extensive skin tumours. Spontaneous mutations occur without exposure to any obvious mutagenic agent. Sometimes DNA nucleotides shift without warning to a different chemical form (known as an isomer) which in turn will form a different series of hydrogen bonds with its partner. This leads to mistakes at the time of DNA replication. SEX DETERMINATION Sex is determined by the sex chromosomes X and Y. The X and Y chromosomes differ in size; the X chromosome is much longer than the Y chromosome. A woman's chromosomes are both alike and are called X chromosomes. She has genotype XX A man has only one X chromosome and the smaller Y chromosome. He has the genotype XY. When meiosis takes place in the female ovary, each ovum receives one X chromosome, so all the ova are the same., i.e. X X, Meiosis in the male testes results in 50% of the sperm getting one X and 50% getting one Y chromosomes.  If an X sperm fertilizes the ovum, the zygote will be XX and grow into a girl. If a Y sperm fertilizes the ovum, the zygote will be XY and grow into a boy. Sex Determination Crossing SEX LINKAGE The X and Y chromosome do not only determine sex, but they also have other genes on them. Some genetic disorders affect many more males than females. E.g., Haemophilia and colour blindness. These diseases are called sex linked diseases. Sex linkage results from the fact that the X chromosome is longer than the Y chromosome.  The presence of a recessive allele on a region of an X chromosome, which does not have a corresponding region on the Y chromosome, will result in the appearance of the recessive trait in the phenotype. This is why sex-linked recessive conditions appear only in males and not females. Sex Linkage: e.g. Haemophilia It is a human disease in which blood is slow to clot. The gene controlling the condition is situated on the X chromosome in the non-overlap region with the Y chromosome. The genes appear in two forms: normal (dominant) and haemophilia (recessive) LET: H represent normal allele for blood clotting (dominant) & h represent allele for haemophilia (recessive) VARIATION Variation is the degree of differences between a set of parents and off-springs. These variations could be inherited or due to external factors: e.g., temperature, light, and moisture for plants. Discontinuous Variation  In a population there are certain characteristics which show a limited form of variation.  Discontinuous variation produces individuals showing clear cut differences with no intermediates in between them. Example: Blood groups in humans (A, B, AB, O), the wing length of drosophila, sex in animals and plants (males & females), sex is inherited in a discontinuous way, it cannot be altered. Continuous Variation In continuous variation the characteristics in a population show a complete gradation (progression) from one extreme to other without any break. Characteristics resulting in continuous variation are produced by the combined effects of many genes & environmental factors. Examples: Height, Weight, Colour of organism, intelligence etc. NATURAL SELECTION It is the process whereby the natural environment favours those organisms showing the best adapted phenotypic variations. It eliminates those individuals that cannot cope the challenges of their environment. These organisms pass their genes onto the nex