Calderglen High School National 5 Biology Unit 2 Multicellular Organisms 1
Sub topic: Producing new cells Chromosomes are found in the nucleus of the cell and carry coded instructions called genes from one generation of cell to the next. When most plant and animal cells divide, their nuclei pass through the same series of changes, called mitosis. A cell chromosomes nucleus chromatid centromere A chromosome Image BBC Bitesize Keeping the chromosome number correct Each species of plant and animal has a characteristic number of chromosomes in the nucleus of each of its body cells which is always the same for the specific species. For example, the body cells of human beings contain 46 chromosomes. Mitosis provides new cells for growth and repair of damaged cells and maintains the diploid chromosome complement. 2
Summary of the stages of mitosis The diagram below represents stages in the process of mitosis in the correct sequence. After a period of growth, mitosis starts again each cell Chromosomes become visible in the nucleus. Two identical daughter cells have been produced. Chromosomes shorten and appear as chromatids joined at the centromere Spindle fibres pull chromatids to opposite ends of the cell. Nuclear membrane disappears and the chromosomes line up along the equator of the cell. 3
Stem Cells Stem cells in animals are unspecialised cells that are involved in growth and repair. They are able to: reproduce themselves by repeated mitosis while remaining unspecialised. develop into various types of specialised cells when required e.g. red blood cell, nerve cell or bone cell. Liver Bone Nerve Image BBC Bitesize Red blood cell Possible uses of stem cells include the treatment of diabetes and cancer, repair to body organs including bone and the windpipe or even the growth of organs for transplant such as liver and skin. Cell organisation Specialisation of cells leads to the formation of a variety of cells, tissues and organs. Groups of organs which work together form systems. The cells are organised in the hierarchy as shown below Cells Tissues Organs Systems Organisms Eg muscle and bone. Eg liver, eye or stomach Eg circulatory system, digestive system 4
Sub topic: Control and Communication In a multicellular organism, cells communicate using nerve impulses or hormones. Nervous control The brain and spinal cord are made of neurons. The brain and the spinal cord make up the central nervous system (CNS). Many nerves join with the CNS. They bring messages as nerve impulses from sensory organs which contain cells called receptors. The CNS sorts this information and processes it. To trigger a response, a different group of nerves are used to carry messages from the CNS to effectors which are usually muscles. image bbc bitesize 5
The Brain The brain plays a very important part in the way you respond to any factors that may affect your body. Just to read this page, millions of nerve messages are zipping around within your own brain. The brain itself is made up of several different parts or regions, each with its own specialised function. image bbc bitesize Part of the brain Cerebrum Cerebellum Medulla Function Controls conscious actions, as well as reasoning and learning. Balance and muscle co-ordination Controls the rate of breathing and heartbeat. 6
Neural pathways This involves three types of neurons. Neurons are highly specialised because they carry electrical impulses, they do not come in contact with one another: A sensory neuron which carries electrical impulses from a sense organ to the CNS. A relay neuron which is located in the brain or spinal cord. It receives electrical impulses from the sensory neuron and transmits them to other neurons involved in the response. A motor neuron which receives electrical impulses from relay neurons and transmits them to a muscle or gland which will carry out the response. When stimulated by an electrical impulse, muscles respond by contract and glands by releasing chemicals. Muscle responds more rapidly than glands. Reflex actions are fast responses that do not normally involve conscious thought. They usually protect your body from harm. Examples of reflex actions include sneezing when foreign particles enter the nose, withdrawal of a hand from a hot object, blinking when an object moves near the eye. The circuit of the neurons that act to produce the reflex action is called the reflex arc (refer to the diagram on the next page) Relay neuron Sensory neuron Image from BBC Bitesize Motor neuron muscle Reflex arc Burning candle 7
The transmission of a nerve impulse through a reflex arc is called a reflex action. In the example above the sensory neuron in the hand detects the heat and this initiates an electrical impulse which travels towards the relay nerve. The impulse is transferred to the rely nerve which passes on the impulse to the motor nerve. The nerve impulse travels along the motor nerve to the muscle which brings about a muscle contraction and the hand is withdrawn from the heat. The neurons do not touch, there is a small gap called a synapse between neurons which allows chemicals to transfer from one neuron to another. Sensory neuron Relay neuron Motor neuron Synapse (gap between neurons) Synapse (gap between neurons) Hormonal control Hormones are made up of proteins. They are chemical messengers which pass on information to target tissues which have special receptor cells sensitive to that specific hormone. Only some tissues are affected by specific hormones. Glands which release hormones into the bloodstream are known as endocrine glands. Endocrine system Image from BBC Bitesize Pancreas Testes (male) Ovary 8
Regulation of Blood Glucose Level in the Blood Cells are constantly using up glucose present in the bloodstream for energy. A rise in blood glucose concentration is detected by cells in the pancreas. These cells produce the hormone insulin. This hormone is transported in the blood to the liver where it activates glucose to be converted to glycogen. This brings blood glucose concentration down to around its normal level. Scran image If the blood glucose concentration drops a different set of cells in the pancreas detect this change and release the hormone glucagon into the bloodstream. This second hormone is transported to the liver and activates the conversion of glycogen to glucose. The blood glucose concentration therefore rises to its normal level. Regulation of Blood Glucose levels Insulin produced when blood glucose level is above the normal level blood glucose level Glycogen in the liver Glucagon is produced when the blood glucose level falls below the normal level 9
Sub topic: Reproduction Diploid Cells After fertilisation, a zygote (fertilised egg) is formed. The cell is DIPLOID A diploid cell has 2 sets of chromosomes (in humans this is 46 chromosomes). One set has come from the male parent and one set has come from the female parent. Every body cell has a copy of the chromosomes that was in the zygote. Therefore, every body cell is a diploid cell. The diploid number in humans is 46. Haploid Cells Eventually, the adult will produce sex cells. Another name for the sex cells is GAMETE. Gametes will only have one set of chromosomes. A HAPLOID cell has only one set of chromosomes The haploid number in humans is 23. Fertilisation Fertilisation is the fusion of the nuclei of the two haploid gametes to produce a diploid zygote, which divides to form an embryo. Haploid Gamete eg sperm Haploid Gamete eg egg Fertilisation produces a diploid zygote 10
Gamete Production in Animals Like plants, animals produce gametes in sex organs. In human males, SPERM are produced in the TESTES. In human females, EGGS (ova) are produced in the OVARIES. Millions of sperm cells are produced in the testes and are able to swim in fluid using their long tails. Egg cells are the largest human cells because of the large food store in the cytoplasm. Sperm (male gamete) head Egg (female gamete) Cell membrane tail nucleus Cytoplasm containing a food store Scran images 11
Animal Reproductive System Male reproductive system image bbc bite size sperm duct penis Testes Female reproductive system image bbc bitesize ovary womb Sexual Reproduction in Plants Flowers are the organs of sexual reproduction in plants. The flower contains both the male and female parts. The ANTHER and FILAMENT together is known as the STAMEN. This is the male parts of the flower. The male anther is the site of gamete production. The diploid anther cells produce the haploid pollen grains, which contain the male gametes. The OVARY is the female part of the flower. The female ovary is the site of gamete production. The diploid ovary cells produce haploid eggs (the female sex cell or gamete). 12
Sub topic: Variation and Inheritance A characteristic shows DISCRETE VARIATION if it can be used to divide up the members of a species into two or more distinct groups. Humans can be split up into two groups depending on their ability to roll their tongue and into four groups based on blood group types A, B, AB and O. Data obtained from a survey of a characteristic that shows discrete variation is represented by a bar chart Discrete variation graph Image bbc bitesize Some characteristics are controlled by the alleles of a single gene they are expressed as clear-cut PHENOTYPIC groups showing discrete variation. In humans, the ability to roll the tongue is an example of the single gene inheritance. In pea plants, the possession of lilac or white flowers is an example of single gene inheritance. 13
Continuous Variation A characteristic shows continuous variation when it varies amongst the members of a species in a smooth, continuous way from one extreme to another and does not fall into distinct groups. CONTINUOUS VARIATION can be represented by a normal DISTRIBUTION CURVE (the curve would be bell shaped). Image bbc bitesize Few individuals show values close to the extremes of the range. Most individuals show values close to the middle of the range (also known as the average). Some characteristics are controlled by the alleles of several genes. This results in the characteristic being expressed as a range of PHENOTYPES e.g. Human height. A characteristic showing CONTINUOUS VARIATION controlled in this way by more than one gene is said to show polygenic inheritance. Phenotypes and Dominant Genes For every characteristic we have 2 genes one from our mother and one from our father. Genes are part of chromosomes. Each characteristic is controlled by two forms of a gene. Each parent contributes one form of the gene. Each gamete (sex cell) carriers one of the two forms of the gene. Differing forms of a gene are called ALLELES. Example The alleles for the gene for eye colour are blue, brown, green, etc. PHENOTYPE this is the physical appearance resulting from the inherited information. Example Someone with blue eyes has the phenotype blue eyes. Genes or alleles can be said to be DOMINANT (shows up in the phenotype) or RECESSIVE (hidden when it is present along with the dominant gene). 14
GENOTYPE this is the combination of genes in a gene pair. Genotype is represented by 2 letters (one letter for each gene). Dominant black gene Recessive white gene Note the phenotype of this individual is Black Hair If the 2 alleles that an organism possesses for a characteristic are identical, the organism is said to be HOMOZYGOUS for the characteristic. BB has a phenotype black it is said to have a HOMOZYGOUS genotype. Homozygous is often called pure breed or true breeding. Bb has the phenotype black but it is said to have a HETEROZYGOUS genotype. If the 2 alleles that an organism possesses for a characteristic are different, the organism is said to be HETEROZYGOUS for that characteristic. bb has the phenotype white and is said to be HOMOZYGOUS recessive. 15
Genetic Crosses A genetic cross is laid out as follows: A pea plant which produces round pea seeds is crossed with a pea plant which produces wrinkled pea seeds. All the offspring are round. R: Round r: Wrinkled Parents Phenotype (P) Round X Wrinkled Parents Genotype (P) RR X rr Gametes First Generation (F1) Genotype First Generation (F1) Phenotype R X r Rr Round F1 X F1 = Gametes Rr X Rr R, r R, r Genotype RR Rr Rr rr Second Generation (F2) Phenotype Second Generation (F2) Round Round Round Wrinkled F2 Phenotypic ratio 3 : 1 The actual ratio may differ from the expected ratio since fertilisation is a random process. An element of chance is involved. 16
Sub topic: Transport systems in Plants Plant organs are roots, stems and leaves. Transport of water in plants Root Hair Cell Image BBC Bitesize The root hair is an extension of the root cell and water is taken in by osmosis through the cells selectively permeable membrane. When this cell has taken on a reasonable amount of water it will have a higher water concentration than the next cell and so water will pass to this next cell by osmosis. This process continues until the water reaches specialised water transport vessels called xylem. Image BBC Bitesize Root epidermal cell Xylem vessel Water travels across the root cortex cells by osmosis and then enters the xylem vessels. 17
Xylem Water and minerals are transported from the roots upwards to the leaves. Xylem forms when the nucleus and end walls of Rings of lignin the cells disintegrate forming long hollow (give plant lignified tubes. Xylem is a non-living material. support) Image BBC Bitesize Water movement in xylem vessels Transpiration is the evaporation of water from the mesophyll cells in the leaves of plants. Water evaporates through stomata whose opening and closing is controlled by guard cells, which are found in the leaf epidermis (outer layer of cells). In order to replace this lost water, water is pulled up through the xylem vessels. Mesophyll cells in the leaf require water for photosynthesis and this is delivered via the xylem vessels. Section of leaf Mesophyll cell in the leaf Xylem Air space in leaf Lower epidermis Stoma Guard cell Image BBC Bitesize 18
Factors affecting transpiration The following factors affect the rate of transpiration; temperature, humidity, air movement and light. These factors are known as abiotic factors. Factor affecting Transpiration rate transpiration rate Temperature Surface area of leaf Wind speed An increase in any of these factors will result in an increase in the rate of transpiration Humidity An increase humidity will result in decrease in the rate of transpiration Opening and closing of stomata When the guard cells become turgid this forces the stoma open. When the guard cells are flaccid the stoma closes. guard cells stoma epidermis Stoma open Stoma closed Images BBC Bitesize 19
Diagram of a leaf showing the position of the stoma. Image BBC Bitesize stoma Transport of sugar in plants Sugar is transported up and down the plant in living phloem cells. Sieve plate Image -BBC Bitesize Companion cell Sieve cell Differences between Xylem and phloem Xylem Transports water and minerals dead lignified No companion cell No sieve plates Phloem Transports sugar living Not lignified Companion cell Sieve plates 20
Sub topic: Transport Systems in Animals Blood consist of two parts The role of blood Blood consists of blood cells and the fluid that surrounds them called plasma. Many substances are transported dissolved in plasma including glucose and amino acids. Plasma Other blood cells Red blood cells White blood cells are part of the immune system and are involved in destroying pathogens (disease causing micro organisms). There are two main types of cells involved: Phagocytes carry out phagocytosis by engulfing pathogens Lymphocytes which produce antibodies which destroy pathogens. Each antibody is specific to a particular pathogen. Red blood cells transport oxygen from the lungs to body cells. The pigment haemoglobin found in the red cells reacts with oxygen at the lungs to form oxyhaemoglobin. At the tissues the oxygen is released to diffuse into the cells. Red blood cells have no nucleus In order to maximise the space available to carry oxygen. They are very small to fit through the smallest blood vessels and have a biconcave shape that increases their surface area. Image source SCRAN Red blood cells In mammals the main transport system is the circulatory system, comprising of the heart and associated blood vessels. The heart is a muscular pump, pumping blood around the body to deliver nutrients and oxygen as well as dispose of carbon dioxide and waste. The wall of the left ventricle is thicker than that of the right because it has to pump blood all round the body. 21
Structure of the heart Valve at exit to pulmonary artery Valve at exit to aorta Right atrium Left atrium Right ventricle Left ventricle Image from BBC Bitesize Valves between atria and ventricles Valves in the heart and in veins prevent the backflow of blood 22
Circulation Pulmonary vein Pulmonary artery aorta Vena cava Image from BBC Bitesize Deoxygenated blood Oxygenated blood The Coronary artery The first branch of the aorta leaving the heart is the coronary artery and this supplies the heart muscle with oxygenated blood. The diagram on the right also shows how a build up of lipid material called plaques can lead to a coronary heart attack. A heart Coronary artery 23
Blood Vessels Arteries carry blood away from the heart. They have a thick muscular wall and a narrow central channel. The blood in arteries is under high pressure. Veins carry blood towards the heart they have a thinner muscular wall than arteries and a wider central channel. The blood in veins is under low pressure and they contain valves to prevent backflow of blood. Artery Vein Valve Thick muscular wall Wide cental channel narrow central channel Thin muscular wall Capillary Thin central channel Capillaries are exchange vessels. Their walls are only one cell thick to allow materials to cross from tissues to capillaries easily. There is a dense network of capillaries giving a large surface area. Examples of materials that cross capillary walls are oxygen and glucose into cells and carbon dioxide and urea from cells to the capillary. 24
Sub topic: Absorption of materials Oxygen and nutrients from food must be absorbed into the bloodstream to be delivered to cells for respiration. Waste materials such as carbon dioxide must be removed from cells into the bloodstream to be removed from the body. Tissues contain capillary networks to allow the exchange of materials at a cellular level. Surfaces involved in the absorption of materials have certain features in common, these include: A large surface area Thin walls Extensive blood supply All these features increase the efficiency of absorption. Function of the lungs At the lungs gas exchange takes place. Carbon dioxide diffuses from capillaries into the alveoli and oxygen diffuses from the alveoli into the capillaries. The Lungs lung airways inside the lungs alveoli 25
Deoxygenated blood Air in Air out Oxygenated blood Alveolus and the large capillary network An alveolus showing gas exchange Image from scran deoxygenated blood oxygenated blood O 2 CO 2 Red blood cell 26
Feature of a gas exchange surface Feature large surface area thin lining surrounded by large capillary network Function to absorb oxygen eases diffusion of oxygen into blood to pick up and transport oxygen Digestive System small intestine Image from SCRAN Image BBC Bitesize The small intestine s internal surface is folded and has thousands of finger like projections called villi. The large number of thin walled villi provides a large surface area. Each villus contains a network of capillaries to absorb glucose and amino acids and a lacteal to absorb fatty acids and glycerol. 27
Structure of a villus Thin wall of the villus Blood capillary absorbs glucose and amino acids Lacteal Absorbs fatty acids and glycerol Image Scran Image from SCRAN 28