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National 5 Biology Course Notes Unit 2 : Multicellular Organisms Part 1 : Cells, tissues and organs Tissues Tissues are groups of cells that have the same structure and function. Each tissue consists of similar specialised cells. Organs An organ is made up of different types of tissue e.g. the heart The heart is an organ that pumps blood around the body It is composed of several tissues, e.g. Muscle Nervous tissue Blood e.g. ciliated epithelium in the windpipe – specialised to sweep dust out of the windpipe A plant organ – the leaf A leaf is an organ whose function is photosynthesis. The diagram shows the layers of cells found inside the leaf Leaf tissues Upper epidermis Palisade mesophyll Spongy mesophyll Lower epidermis The leaf also contains two transport tissues xylem(transports water) and phloem (transports sugar) in the leaf veins Summary of organisation of cells in multicellular organisms Are grouped together in CELLS TISSUES Several different tissues are found in an ORGAN Groups of similar cells with the same function Organs with similar functions are grouped into ORGAN SYSTEMS For example, the digestive system, the nervous system National 5 Biology Course Notes Unit 2 : Multicellular Organisms Part 2 : Cells, tissues and organs Stem cells Stem cells are found in animals. They can 1. Divide by mitosis to provide more stem cells 2. Differentiate (develop into specialised cells). Types of stem cells Two types depending on where they are found 1. Embryonic stem cells These are found in embryos They can develop into any type of body cell They produce cells for growth of the embryo 2. Adult (tissue) stem cells Found in fully formed animals (babies and children as well as adults) They can develop into a limited range of cell types, e.g. stem cells found in bone marrow can only become blood cells They produce cells for repair of the body Potential uses of stem cells and ethical issues Stem cells have current and potential medical uses. Since embryonic stem cells can become any type of cells, they are potentially the most useful but there are ethical issues involved in their use since the embryos are destroyed to get the cells. Meristems Meristems are areas of plants that contain cells that divide by mitosis to produce new cells for growth of the plant. In plants cells that divide are found only at meristems and the unspecialised cells produced can become any type of plant cell. Meristems are found • At the root and shoot tip – these produce new cells for increase in length of the root and shoot • Between the xylem and phloem – these meristems produce new cells for increase in thickness of the root and shoot Meristems at the shoot and root tips provide new cells for growth in the length of the root and shoot Meristem between the xylem and phloem provides new cells for growth in thickness of the root and shoot National 5 Biology Course Notes Unit 2 : Multicellular Organisms Part 3 : Control and communication Nervous control Central nervous system (brain and spinal cord) The nervous system The nervous system consists of: • The central nervous system (CNS) – the brain and spinal cord • The peripheral nervous system – all the other nerves Peripheral nervous system Structure and function of the brain Part of the brain cerebrum cerebellum medulla Function cerebrum Thoughts, memories, reasoning, receives messages from sense organs, conscious muscle control cerebellum Controls balance medulla Control of involuntary actions, e.g. heartbeat, breathing rate Neurons Neurons are nerve cells. There are three kinds of neurons: Sensory neurons These carry nerve impulses from sense organs to the central nervous system Motor neurons These carry nerve impulses from the central nervous system to muscles and glands Relay neurons Found in the central nervous system. Carry nerve impulses from sensory neurons to motor neurons. Reflex actions Reflex actions are • fast • inborn – don’t have to be learned • carried out in the same way be all members of the species • for protection Examples of reflex action • Pupil size decreasing in bright light • Sneezing when dust enters the nose • Pulling hand away from a very hot object Reflex arc A reflex arc is the path followed by a nerve impulse when carrying out a reflex action. A stimulus is detected by a receptor, e.g. receptors in the skin detect a hot object A nerve impulse passes along a sensory neurone to the central nervous system A nerve impulse passes along a relay neurone in the central nervous system The effector responds (e.g. the muscle contracts and pulls the hand away from the hot object) A nerve impulse passes along a motor neurone to a muscle Effectors Sensory cells in skin Sensory neurone synapse Spinal cord Relay neurone muscle Motor neurone Effectors can either be muscles bringing about a fast response, for example when the hand is pulled away from a hot object or glands bringing about a slow response, e.g. sweat glands producing sweat when the temperature increases. Synapse Where two nerve cells meet, there is a microscopic space between them called a synapse. When a nerve impulse reaches the end of the first neurone, it causes release of a chemical that triggers a nerve impulse in the second neurone. End of first neurone Synapse Start of second neurone Nerve impulse reaches the end of the first neurone This causes release of a chemical that diffuses across the synapse And triggers a nerve impulse in the second neurone Hormones As well as the nervous system, parts of the body can communicate through hormones. Hormones are chemical messengers produced by endocrine glands. The endocrine glands release their hormones directly into the blood as it flows through the gland. Hormones travel around the body in the blood but they have an effect only in certain parts called the target tissues of the hormone. This is because the target tissues have receptors on their cells that the hormone can bind to. Control of blood glucose Blood glucose is controlled by two hormones produced in the pancreas called insulin and glucagon. Blood glucose increases after eating Blood glucose decreases after fasting Pancreas releases insulin into the blood Pancreas releases glucagon into the blood Insulin reaches the liver Glucagon reaches the liver Liver changes glucose in the blood to glycogen and stores it Blood glucose level decreases back to normal Liver changes stored glycogen into glucose Blood glucose level increases back to normal Diabetes Diabetes results either from the body producing no insulin or too little insulin (type 1 diabetes) or from body cells not responding to insulin (type 2 diabetes). Type 1 diabetes is treated by insulin injections while type 2 may be treated by lifestyle changes, e.g. healthy diet and exercise. Untreated diabetes can result in damage to small blood vessels especially of the eyes and kidneys resulting in blindness and/or kidney failure. National 5 Biology Course Notes Unit 2 : Multicellular Organisms Part 4 : Reproduction Reproduction Body cells are diploid. The fertilisation of haploid gametes to produce a diploid zygote. Body cells have 2 sets of chromosomes (one set comes from each parent) – these cells are diploid. Sex cells are called gametes, they have one set of chromosomes and are said to be haploid. Fertilisation Fertilisation occurs when a male and a female gamete fuse. The cell produced by fusion of gametes is called a zygote. The zygote is diploid Haploid male and female gamete fertilisation Diploid zygote The structures and sites of gamete production in plants and animals Flowering plants The diagram shows structures in a flower Pollen grains, which contain the male gamete, are produced in the anther anther ovules ovary Ovules, which contain the female gamete are produced in the ovary Mammals Male gametes (sperm cells) are produced in the testes Female gametes (eggs) are produced in the ovaries testis ovary Comparison of discrete and continuous variation Most features of an individual phenotype are polygenic and show continuous variation. Identification of phenotype and genotype, dominant and recessive characteristics and homozygous and heterozygous individuals. Comparison of discrete and continuous variation Discrete variation Characteristics that show discrete variation are those that have clear cut differences which allow a member of a species to be put into a particular distinct group. Examples of characteristics in humans that show discrete variation are: Gender Right or left handed Tongue roller or non-roller Attached or unattached ear lobes Continuous variation These characteristics show slight differences between individuals between an extreme upper and lower value Examples of characteristics in humans showing continuous variation are Height Body mass Hand span Foot length What type of variation is shown by these characteristics Round or wrinkled seed in pea plants Discrete variation Milk yield in cattle Continuous variation Blood group in humans Discrete variation Resting heart rate in humans Continuous variation Identification of phenotype and genotype, dominant and recessive characteristics and homozygous and heterozygous individuals. Phenotype The characteristics an organism has / its appearance Genotype The genes that an organism has for a characteristic Alleles Different forms of a gene / different genes for the same characteristic, e.g. the gene for blue eyes and the gene for brown eyes are alleles Homozygous Having two identical genes for a characteristic Heterozygous Having two different alleles for a characteristic Dominant The gene that is expressed in the phenotype of a heterozygous individual Recessive The gene that is masked (not expressed) in the phenotype of a heterozygous individual True breeding A true breeding individual is homozygous for the characteristic Most features of an individual phenotype are polygenic and show continuous variation. Polygenic A characteristic that is controlled by many genes is described as polygenic. Characteristics showing continuous variation are polygenic. Most of an organism’s characteristics are polygenic Two parents with the characteristic resulting from the dominant gene can produce offspring (children) with the recessive characteristic But Two parents with the recessive characteristic cannot produce offspring with the dominant characteristic Male with attached ear lobes Male with free ear lobes Female with attached ear lobes Which characteristic is controlled by the dominant gene? An individual with the recessive characteristic must have two recessive genes What is the genotype of the son who has free ear lobes? An individual receives one gene for a characteristic from each parent and passes one gene for each characteristic on to each offspring What is the genotype of the two parents? Transport in plants – what the syllabus says you should know Plant transport systems i. Water is required for transporting materials and for photosynthesis. ii. Structures and processes involved in water movement to include root hairs, guard cells, stomata, epidermis, mesophyll cells and transpiration • • • • Transpiration is the loss of water through leaves. Water is lost by evaporation through stomata. Opening and closing is controlled by guard cells, which are found in the leaf epidermis. Mesophyll cells of the leaf require water for photosynthesis. Water and minerals are transported up through the stem in xylem. Xylem cells are lignified. • Xylem cells are lignified to withstand the pressure changes as water moves through the plant. iii Sugar is transported up and down the plant in living phloem cells. Water is required for transporting materials and for photosynthesis. Plants need water 1. To transport dissolved substances such as minerals 2. As a raw material for photosynthesis Structures and processes involved in water movement to include root hairs, guard cells, stomata, epidermis, mesophyll cells and transpiration Root hairs Root hairs are extensions of cells on the outer layer of the root (called the epidermis) Root hairs 1. Anchor the root in the soil 2. Increase it’s surface area for absorbing water Root hairs Guard cells Guard cells A leaf has pores called stomata mainly on it’s lower surface. Each pore (stoma) is surrounded by 2 guard cells. Guard cells control the opening and closing of the stomata. The guard cells are part of the epidermis tissue of the leaf. stoma Epidermis cells Structures and processes involved in water movement to include root hairs, guard cells, stomata, epidermis, mesophyll cells and transpiration Diagram showing guard cells surrounding the stoma Stoma Guard cell Epidermis cell Structures and processes involved in water movement to include root hairs, guard cells, stomata, epidermis, mesophyll cells and transpiration Leaf cells The photo shows the layers of cells in a plant leaf This part contains palisade mesophyll cells where most photosynthesis in the leaf takes place This part contains spongy mesophyll cells where some photosynthesis takes place Water and minerals are transported up through the stem in xylem. Xylem cells are lignified to withstand pressure changes as water moves through the plant Xylem Water is transported from the roots up through the plant to the leaves in tubes called xylem vessels Xylem vessels are lignified – this means they have a substance called lignin in their walls, usually in the form of lignin rings Lignin allows the vessels to cope with pressure changes as water moves through the plant. Xylem also transports minerals dissolved in the water and in addition helps to support the plant. Xylem vessels are made from dead cells Xylem vessels showing lignin rings Transpiration is the loss of water through leaves. Water is lost by evaporation through stomata. Opening and closing is controlled by guard cells, which are found in the leaf epidermis. Mesophyll cells of the leaf require water for photosynthesis. Transpiration Diagram of leaf cells Transpiration is loss of water through the stomata of the leaves Palisade and spongy mesophyll cells 1. Water evaporates into air spaces in the leaf 2. Water diffuses out of the leaf through the stomata Opening and closing of the stomata is controlled by the guard cells The stomata are open in light and closed in darkness Transpiration helps to pull water up from the roots to the leaves The leaf mesophyll cells need the water to carry out photosynthesis 1 Guard cell 2 Movement of water through the plant Water enters leaf cells Water evaporates from leaf cell surface into air spaces in the leaf Water vapour diffuses out of the leaf Water enters root hair cell from soil by osmosis Water is drawn up through the xylem vessel by transpiration in the leaf Water passes across the root from cell to cell and into a xylem vessel by osmosis Loss of water through the stomata is called transpiration Sugar is transported up and down the plant in living phloem cells. Phloem Phloem is a plant tissue composed of living cells in which sugar is transported Phloem has two types of cells • Sieve tubes • Companion cells Perforated sieve plate Sieve tubes have no nucleus and their separating walls (called sieve plates) have holes that allow strands of cytoplasm to run from one cell to the next. Companion cells have a nucleus and they control the sieve tubes. Sugar moves through the sieve tubes from the leaves where it is made by photosynthesis to other parts of the plant where it is used for respiration or to parts where it is stored, e.g. fruits. Sieve tube Companion cell Heart – syllabus content Multicellular organisms need transport systems to deal with surface area to volume ratio issue. Animal transport and exchange systems In mammals, nutrients, oxygen and carbon dioxide are transported in the blood. Pathway of blood through heart, lungs and body. Heart structure to include right and left atria and ventricles. Blood vessels to include: aorta, vena cava, pulmonary arteries and veins, and coronary arteries. Arteries have thick, muscular walls, a narrow central channel and carry blood under high pressure. Veins carry blood under low pressure; have thinner walls and a wide channel. Veins contain valves to prevent backflow of blood. Capillaries form networks at organs and tissues, and are thin walled and have a large surface area, allowing exchange of materials. Red blood cells contain haemoglobin and are specialised to carry oxygen Heart structure to include right and left atria and ventricles. Structure of the heart Chambers of the heart Left atrium Right atrium Right ventricle Left ventricle Note: The left ventricle has a thicker wall (more muscle in its wall) than the right ventricle because it pumps blood further Blood vessels to include: aorta, vena cava, pulmonary arteries and veins, and coronary arteries. Blood vessels entering and leaving the heart Blood to the body Pulmonary artery Blood to the lungs Aorta Vena cava Blood from the lungs X x Position of heart valves Blood coming from the body X X Pulmonary vein Blood supply to the heart itself The heart tissue receives blood from the coronary arteries Right coronary artery Left coronary artery Arteries have thick, muscular walls, a narrow central channel and carry blood under high pressure. Veins carry blood under low pressure; have thinner walls and a wide channel. Veins contain valves to prevent backflow of blood. Vein structure Artery structure Thick layer containing smooth muscle Thin layer containing smooth muscle Narrow channel Wide channel Arteries Veins Take blood away from the heart Take blood back to the heart Have thick muscular walls and a narrow lumen - blood is under high pressure Have thin walls and a wide lumen - blood is at low pressure No valves Have valves to prevent backflow of blood Capillaries form networks at organs and tissues, and are thin walled and have a large surface area, allowing exchange of materials. Capillaries Capillaries are very small, thin walled vessels that are found close to all body cells Substances are exchanged between the blood and cells through the capillary walls Capillary beds Body cells are found close to capillaries in capillary beds Substances like glucose and oxygen pass by diffusion from the blood in the capillaries to the liquid around the cells then into the cells. Carbon dioxide diffuses in the other direction Glucose and oxygen Carbon dioxide capillary Tissue fluid Body cells Capillaries have a large surface area and thin walls to allow efficient exchange of substances Red blood cells contain haemoglobin and are specialised to carry oxygen Oxygen is transported in red blood cells Red blood cells contain a substance called haemoglobin. When the oxygen concentration is high (in the lung capillaries), haemoglobin joins with oxygen to make oxyhaemoglobin Oxygen is carried in the blood joined to haemoglobin When the oxygen concentration is low (in the body capillaries) oxyhaemoglobin breaks down again to release the oxygen for the body cells. in lung capillaries Haemoglobin + oxygen in body capillaries oxyhaemoglobin National 5 Biology Course Notes Unit 2 : Multicellular Organisms Part 8 : Effect of lifestyle choices on animal transport systems These lifestyle choices can have a harmful effect on the heart and blood vessels 1. 2. 3. 4. 5. 6. A high fat diet A high salt content in the diet Lack of exercise Smoking tobacco Excessive alcohol drinking Stress These directly and indirectly increase the chance of fat deposits forming in blood vessels, blood clots, heart attacks, strokes and type II diabetes. Fat deposits in artery walls narrow the vessels and restrict blood flow. This and blood clots block arteries stopping blood flow and causing heart attacks and strokes Anaemia The mineral iron is needed to make haemoglobin. Deficiency of iron in the diet leads to anaemia. Environmental factors Environmental factors which pose hazards to our health include; 1. Toxic heavy metals which are found in paint, fuel and old pipes. 2. Carbon Monoxide pollution via vehicle exhausts, faulty gas mains or fires in homes. 3. Radiation from unprotected exposure to the sun including the use of sunbeds.