National 4 Biology Multicellular Organisms

Transcription

1 1 National 4 Biology Multicellular Organisms Notes

2 2 Contents Contents... 2 Sexual Reproduction... 3 Internal Fertilisation... 4 External Fertilisation... 6 Sexual Reproduction in Plants... 7 Plant Pollination and Fertilisation... 8 Germination, Growth and Development... 9 Seed Germination Growth and Development of Different Organisms Life Cycles Growth and Development in Humans Diet Asexual Reproduction Methods of Asexual Reproduction in Plants Advantages of Sexual and Asexual Reproduction Artificial Methods of Asexual Propagation of Plants Advantages of Artificial Propagation in Flowering Plants Commercial Uses of Plants Genetic Information Discrete and Continuous Variation Forms of Genes (Alleles) Dominant and Recessive Alleles Punnett Squares True Breeding Genetic and Environmental Factors Environmental Variation Maintaining Stable Body Conditions The Nervous System The Central Nervous System Sensory and Motor Neurones Sensory Receptors Homeostasis Part 1 Maintaining Body Temperature The Skin Homeostasis Part 2 Maintaining Blood Sugar Levels... 36

3 3 Sexual Reproduction Sexual reproduction is when two parents or sex cells are involved in producing a new member of the species. Sexual reproduction leads to variation (differences) in offspring. In animals, males and females produce sex cells. Sex cells are called gametes. Male gametes are called sperm. Female gametes are called eggs. Fertilisation Sperm and eggs fuse together to produce a new member of the species. This fusion, joining together, is called Fertilisation. In animals the egg (ovum) is large with a food store. It cannot move on its own. The sperm is small with no food store and can swim. The sperm swims towards an egg and fertilisation takes place. Fertilisation is the fusing of the nuclei of sperm and egg to form a fertilised egg cell called a zygote. Chromosomes In humans, eggs and sperm have 23 chromosomes each. At fertilisation, a zygote (a fertilised egg cell) with 46 chromosomes is formed. The 23 chromosomes from the sperm join up with the corresponding 23 chromosomes from the egg to form 23 pairs of chromosomes..

4 Fertilisation can be internal or external. 4 Internal Fertilisation Internal Fertilisation During internal fertilisation the sperm and egg meet inside the body of the female parent. Examples: humans, other mammals, birds, insects Internal fertilisation is important because it means that animals can live on land. Sperm have to swim through a liquid to meet an egg. Internal fertilisation allows the sperm to swim through liquid inside the female s body. Example of Internal Fertilisation: Reproduction in Humans

5 5 1. Eggs are produced in the ovary. Pregnancy is the time from the fertilisation of the egg by the sperm to the birth of the baby. While it is in the womb, a baby is called an embryo. The embryo grows inside the womb for 9 months. At the end of this time, embryo (the baby) is about 15 centimetres long and weighs about 3 kilograms. The embryo is warm and well protected inside the womb. It grows in a bag of liquid (called amniotic fluid) inside the womb. The embryo is joined up to the placenta by a long tube called the umbilical cord. The placenta is where blood and oxygen from the mother crosses into the baby through the umbilical cord. Waste, such as carbon dioxide and urine, pass from the embryo to the mother.

6 Fertilisation can be internal or external. External Fertilisation 6 External Fertilisation External fertilisation is when the egg and sperm meet outside the female s body. Examples: fish, frogs. Example of External Fertilisation: Reproduction in Sticklebacks The female stickleback produces many eggs. The male stickleback prepares a nest where the eggs will be laid. The male shows he is ready to fertilise the eggs by displaying his red belly and doing a zig-zag dance. The female enters the nest and lays the eggs. She then leaves the nest. The male enters the nest and produces sperm which fertilise the eggs. The eggs are left to hatch. Many eggs have to be produced for external fertilisation to be successful as a way of reproducing young. This is because o o the eggs could be swept away from the sperm before fertilisation can take place. the eggs are not well protected, so many are eaten by predators. Some animals, such as coral and sea urchins, release sperm and eggs at the same time in the same place to increase the chance of fertilisation. This is called spawning. Internal and External Fertilisation Comparison o o o o Not so many sperm are needed for internal fertilisation because there is a good chance that they will meet an egg and fertilise it. Lots of sperm are needed for external fertilisation because of danger in the environment. Internal fertilisation in mammals protects the egg inside the mother s body. Fish eggs, produced by external fertilisation, are protected by only a coat of jelly. Mammals provide food for the embryo through the mother s placenta. In fish, the yolk sac provides food. Mammals protect the embryo inside the body. Fish eggs have no protection.

7 7 Sexual Reproduction in Plants Pollination Pollination happens when pollen transfers from the anther of one flower to the stigma of another flower of the same species.

8 8 Plant Pollination and Fertilisation Pollination by Insects Plant Fertilisation

9 9 Germination, Growth and Development Growth and development of different organisms Growth is the increase in mass of an organism. When an organism grows, it gets bigger. It has more cells. The starchy food store is used for energy during germination. The food store is protected from fungi in the soil by the thick seed coat. The embryo plant grows roots and a shoot. The embryo develops into the new plant.

10 How a plant grows from a seed in the soil The shoot grows out. It is hook-shaped to prevent damage to the tip. 4. The shoot breaks through the surface of the soil. 5. The root continues to grow and the shoot grows up. 6. The plant straightens and the first leaves open out. 2. The root starts growing 7. Side branches grow out from the main root 1. The seed is planted in the soil The life cycle shows the changes which take place. It takes days to reach stage 7.

11 11 Seed Germination Germination is the development of a new plant from the tiny embryo in the plant seed. Plants germinate to become independent, with green leaves to photosynthesise. Before they can germinate, seeds need water, oxygen and warmth. (WOW) o o o Water is needed to let the embryo plant digest the food that has been stored in the seed. Oxygen is needed for respiration. Warmth is needed to allow special chemicals called enzymes to work properly. Plants need these enzymes for growth. Important: Temperature affects the enzymes which control germination. If the temperature is too low, the enzymes work too slowly. If the temperature is too high the enzymes will be denatured. Optimum (best) temperature for germination in Scotland is between 5ºC and 15 C.

12 12 Growth and Development of Different Organisms Life Cycles

13 13 LIFE CYCLE OF A SALMON

14 14 Growth and Development in Humans Diet Your diet is what you eat. A healthy diet gives the body all the nutrients and energy it needs without damaging the body with too much food or damaging substances. Start at the base of the pyramid. You should eat less of the foods shown as you go up the pyramid. So you should eat lots of bread, rice etc. but very little fats, oils, sweets etc. The pyramid gives you an idea of how much you should eat of the various foods per day. People need food to give them energy and nutrients (vitamins, minerals etc.) Different groups of foods do different things which the body needs: Proteins in meat, eggs etc are used for growth and to repair any damage. Vitamins and minerals in fruit, vegetables, etc keep the body working properly. Carbohydrates in bread, rice etc. give the body energy. Fats in oil, butter etc. give the body energy and insulation.

15 15 Asexual Reproduction Asexual means without sex. Asexual Reproduction is a method of producing offspring without the involvement of male and female sex cells. Asexual reproduction means that a parent organism produces a growth which separates itself and becomes an independent organism. Examples: Strawberries Yeast Spider plants Coral and many other sea-creatures Since the offspring comes from only one parent, the genetic information in the new individual is identical to the genetic information in the parent. We call this a clone. All the individuals produced by the same parent will be genetically identical to one another.

16 16 Methods of Asexual Reproduction in Plants 1. Tubers Tubers are parts of the roots which swell up with food to let some plant survive the winter. Each plant can produce a number of tubers. Each tuber grows into a new plant the following year. Example: potatoes 2. Runners Runners are horizontal stems which grow out of the parent plant. They have buds along them which grow into new plants. The parent plant provides food and water for the plantlets (clones) through the runners. Examples: strawberries, spider plants Spider Plant

17 17 Advantages of Sexual and Asexual Reproduction 1. Advantages of Sexual Reproduction Because offspring are produced by two parents, variation in the offspring is possible. This is an advantage because the new organisms can adapt to changes in the environment, so the species has a better chance of survival. Plants usually grow at a distance from the parent plant and at a distance from other offspring from the same parent plant. This gives them more light and space, so they have a greater chance of survival. 2. Advantages of Asexual Reproduction There is no need for pollination. Plants can reproduce without having to depend on insects, wind etc. The parent plant feeds the offspring. This means that the young plant can grow more quickly and so has a greater chance of survival. The environment is the same for the parent and offspring. If the environment suits the parent plant, it will also suit the offspring.

18 18 Artificial Methods of Asexual Propagation of Plants Most of the methods used by plant growers to increase the number of plants artificially depend on the plants being able to regenerate themselves after being damaged. 1. Cuttings A cutting is part of a plant which has been damaged by being cut off and planted in soil. The cutting produces new roots to become a new plant. The cuttings can be taken from stems or from leaves, depending on the type of plant. Sometimes hormones (rooting powder) are added to the soil to help the plant grow roots. Stem Cutting Leaf Cuttings 2. Grafting In grafting, the stem of one plant is joined to the root of another plant. The stem is called the scion. The root is called the rootstock. The scion keeps its own characteristics (type of plant, leaves, fruit etc) but the rootstock can change how big and strong the new plant will be. It provided the plant with nutrients and water. Grafting is used to produce plants with improved features, such as better fruit or flowers. Grafting is normally needed when plants, usually trees or shrubs, do not grow well or when propagation from cuttings is less successful.

19 19 Advantages of Artificial Propagation in Flowering Plants 1. Uniformity All the cutting are genetically identical. They are clones. This is important if you are producing large numbers of plants for sale, for example bunches of roses. 2. Conservation Rare plants can be helped to survive by artificial propagation. 3. New Varieties By artificial reproduction you can change the characteristics of plants to make varieties suitable for your purpose; for example, seedless grapes or oranges with fine peel.

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21 21 Commercial Uses of Plants 1. Food for people The population of the world is growing. Wheat, rice, corn etc has to be grown to feed them. Barley is grown to produce alcohol for beer and whisky. 2. Food for Livestock (cows, pigs etc) Fodder, turnips etc are grown to feed livestock 3. Fuel Sugar cane, sugar beet and maize can be processed to make alcohol. This alcohol is mixed with petrol to power petrol engines. Rapeseed produces oil for cooking. The oil can also used to produce biodiesel for use in diesel engines. The leaves can be used to feed animals. 4. Medicine Poppies are grown to produce morphine for pain relief. Aspirin comes from willow trees. Foxgloves produce digitalis, used to treat heart disease Yew produces taxols, used to treat breast cancer. 5. Timber Scots pine is used for timber in buildings, telegraph poles and railway sleepers Norwegian spruce is used for furniture and skirting boards in houses. 6. Fabrics Cotton, jute and flax are grown to make cloth. The ancient Egyptians grew flax to make linen cloth.

22 22 Genetic Information Characteristics Living things have certain characteristics. Characteristics in humans are things like skin colour, hair colour, height, shape of ears etc. Characteristics in plants are things like flower colour, shape of leaves, height of plant etc. Living things get their characteristics from their parents. They come from the genetic information from the male and female sex cells, the chromosomes which joined together at fertilisation, when the new life began. Living things pass on this genetic information to their offspring. Variation All members of the same species have inherited the same general characteristics. For example, elephants have a trunk, plants have leaves and roots, humans have hair and teeth. But these characteristics are not identical in every member of the species. For example, all humans have hair but some humans have black hair; some have red hair and some have brown hair. This happens because there are very small differences in the genetic information which has passed from parents to offspring. These differences in a characteristic from one individual to another are called variations. Phenotype A phenotype is the name we give to the way the characteristic appears in an individual. Examples: Characteristic Eye colour Flower colour Height Tongue-rolling Phenotypes grey eyes, green eyes, blue eyes, brown eyes red, yellow, white, purple, pink flowers average, taller than average, shorter than average can roll your tongue, cannot roll your tongue

23 23 Discrete and Continuous Variation There are two types of variation Discrete and Continuous. Discrete Variation Discrete variation is variation that has distinct groups for organisms to belong to. There are clear cut differences between individuals. Examples: People who can roll their tongue, people who cannot roll their tongue People with blood type O, people with blood type A, people with blood type AB etc. People with blue eyes, people with brown eyes, people with green eyes etc. Discrete variation is sometimes called discontinuous variation. A bar graph is usually used to show discrete variation. Continuous Variation Continuous variation is variation that is not clear cut. Individuals can be found on a range of the same variation. Examples: Height Skin colour A line graph is normally used to show continuous variation.

24 24 Forms of Genes (Alleles) Characteristics (traits) are inherited from parents. A living being s genotype is the genetic information which has come from its parents. (Genotype is another way of saying genetic information or genes.) Genes are carried on chromosomes. Each body has two matching sets of chromosomes carrying the genes. (One set from the male sex cell and one from the female sex cell. They match up at fertilisation). Alleles Some characteristics, such as eye colour, are controlled by a single gene. These genes can have different forms. Different forms of the same gene are called alleles. For example, the gene for eye colour can have an allele for blue eye colour, brown eye colour, grey eye colour etc. To make up a gene, an offspring inherits one allele for the gene from one of its parents and one allele for the gene from the other parent. So it is possible for an offspring to get one form (allele) of the gene, for example brown eyes, from its father and a different allele of the gene, for example green eyes, from its mother. Homozygous and Heterozygous Organisms can be homozygous or heterozygous for a gene. Homozygous means that the organism has two copies of the same allele for a gene. For example, for the gene eye colour a child might inherit an allele for brown eyes from his father and an allele for brown eyes from his mother. Heterozygous means that an organism has two different alleles of a gene. For example for the gene for eye colour the child might inherit an allele for brown eyes from his father and an allele for blue eyes from his mother. Dominant and Recessive Alleles Some alleles are dominant and some are recessive. (Capital letters are used to refer to dominant alleles. Lower-case letters are used to refer to recessive alleles.) Dominant alleles (dominant characteristics) always out-do recessive alleles. That is, the effect of the dominant allele is seen in the individual. For example, if a child has inherited an allele for brown eyes and an allele for green eyes, and brown eyes is dominant, the child will have brown eyes. Recessive alleles are masked by dominant alleles. The recessive alleles are still there, but you do not see their effect.

25 25 Dominant and Recessive Alleles This means: The characteristic controlled by a dominant allele develops if the dominant allele has been inherited from both parents or just from one parent. The characteristic controlled by a recessive allele develops only if the child has inherited only the recessive allele. (He has not inherited the dominant allele at all.) Remember that an organism inherits one allele (form of a gene) from the father and one allele from the mother. For example, in the gene for shape of hairline, the allele for widow s peak hairline is dominant, shown as W. The allele for not-widow s peak (straight hairline), shown as w, is recessive. A person who inherits even just one allele for widow s peak (the dominant allele, W) will have a widow s peak hairline. A person will only have a straight hairline if he inherits only alleles for not-widow s peak (the recessive allele, w) and no dominant allele at all.

26 26 Punnett Squares Reginald C. Punnett was a scientist who developed a diagram for showing the probability of an offspring (child) inheriting the characteristics of its parents. The diagram is called a Punnett Square. The father s own two alleles are shown along the top of the diagram. (Allele 1 and Allele 2) He has a dominant allele for brown eyes and a recessive allele for eye colour which is another colour. The dominant allele is shown with the capital letter B. The other eye colour is shown with the lower case letter b. The mother s own two alleles are shown down the left hand side of the diagram (Allele 1 and Allele 2). She has two recessive alleles, b, for an eye colour which is not brown. Remember, a child inherits only one allele from each parent. It could be the dominant B (brown eyes) or the recessive b (another colour of eyes). The child could inherit his father s dominant allele for brown eyes, (Allele 1, B and his mother s recessive allele for another colour of eyes (Allele 1, b). He will have brown eyes because he has the dominant allele. Allele 1 Allele 2 The child could inherit his father s dominant allele for brown eyes, (Allele 1,B) and his mother s recessive allele for another colour of eyes (Allele 2, b). He will have brown eyes because he has the dominant allele. Allele 1 Allele 2 The child could inherit his father s recessive allele for othercoloured eyes (Allele 2,b) and his mother s recessive allele for another colour of eyes (Allele 1,b). He will have eyes which are blue or green or grey because he has two recessive alleles. The child could inherit his father s recessive allele for othercoloured eyes (Allele 2,b) and his mother s recessive allele for another colour of eyes (Allele 2,b). He will have eyes which are blue or green or grey because he has two recessive alleles.

27 27 True Breeding When an organism has two of the same forms of a gene they are known as true breeding. Looking at the example below in each case the flower colour of the offspring is always identical to that of the parents. Parental Generation (P) Both parents have inherited two dominant alleles. First Generation Offspring (F1) The parents have passed only the dominant alleles to their offspring because they did not have any recessive alleles. Second Generation Offspring These offspring have also inherited only the dominant alleles. The parent flowers are both true breeding, one for purple flowers and one for white flowers. But when they are crossed, purple flowers is the dominant allele. In a true breeding cross, all the offspring of the first generation are the same as one another. That is they all show the dominant characteristic, purple flowers. The recessive allele has not disappeared. It has just become masked. The characteristics appear in the second generation in the ratio of 3 dominant to 1 recessive.

28 28 Genetic and Environmental Factors Some variation is inherited (genetic), and some variation is due to the environment. Some variation is due to a combination of both genetics and environment. Environmental Variation Characteristics of animal and plant species can be affected by environmental factors like climate diet accidents culture (how things are done in your part of the world) lifestyle (personal choices) For example, if you eat too much you will become heavier, and if you eat too little you will become lighter. Identical twins inherit exactly the same genetic information from their parents. But if you take a pair of twins, and twin A eats more than twin B, twin A is likely to end up heavier. Variations caused by environmental factors are not usually passed from one generation to the next generation. Personal choices make these identical twins look different Variation caused by the conditions is called environmental variation. Other examples of features that show environmental variation: where you stay your language your religion flower colour in hydrangeas (they produce blue flowers in acidic soil and pink flowers in alkaline soil).

29 29 Maintaining Stable Body Conditions The Nervous System The nervous system is made up of three parts: The Brain The Spinal Cord The Nerves The nervous system detects a stimulus in the body and coordinates a suitable response. The response is very rapid. The nervous system uses electrical impulses to bring about fast responses. The electrical impulses travel through the nerve cells. The Brain Cerebrum Controls movement, senses, learning, communication, language, memory Cerebellum Regulates and coordinates movement, posture, and balance Spinal Cord Connects the brain to the nerves throughout the body Medulla Carries out and regulates life sustaining functions such as breathing, swallowing and heart rate

30 30 The Central Nervous System The Central Nervous System (CNS) is made up of The Brain The Spinal Cord. The Central Nervous System sorts out information from the senses. It sends messages to muscles and glands to make appropriate responses. Information is carried to the Central Nervous System from the senses along sensory nerve cells (sometimes called sensory neurones). Information is carried from the Central Nervous System to the muscles along motor nerve cells (sometimes called motor neurones). Sensory neurones (nerve cells) carry signals from the outer parts of your body into the Central Nervous System. Motor neurones (nerve cells) carry signals from the Central Nervous System to the outer parts (muscles, skin, glands) of your body. Interneurones connect various neurons within the brain

31 and spinal cord. 31

32 32 Sensory and Motor Neurones Nerve cells are also called neurones. The diagram above shows a sensory neurone. The diagram above shows a motor neurone. Nerve cells have tiny branches at each end, and a long fibre. This is used to carry electrical signals.

33 33 Sensory Receptors Sensory receptors are found in all parts of the body. They give us our senses. There are lots of different types of sensory receptors. They detect a stimulus from the environment and produce an electrical signal. This signal is picked up by sensory neurones and carried to the Central Nervous System. Examples of sensory receptors: Sight receptors are found in the eyes. They detect light stimulus in the environment. Hearing receptors are found in the ears. They detect sound. Touch receptors are found in the skin and mouth. They detect pressure on the body. Taste receptors are found on the tongue. They detect dissolved chemicals. Smell receptors are found in the nose. They detect chemicals in gases. Balance receptors are found in the inner ears. They detect movement of the head. Temperature receptors are found in the skin. They detect heat moving to and from the skin. Pain receptors are found in the skin, muscles, bones etc. They detect damage to the body. The Reflex Arc Your body tries to keep itself from harm by instantly reacting to harmful outside stimulus. This happens without you having to think. The diagram shows the reflex arc, the instant reaction to damage to a finger from a sharp point. The pain receptors in the finger send out an electrical signal. This is picked up by sensory nerves (sensory neurones) and carried to the spinal cord in the Central Nervous System. A message is sent from the spinal cord to the brain. In the spinal cord the signal is passed to Inter-neurones and from them to motor nerves (motor neurones). The motor nerves carry the signal to the muscles in the arm. The muscle pulls the hand away from the danger.

34 34 Homeostasis Part 1 Maintaining Body Temperature Homeostasis is the way in which a body keeps its internal conditions stable. One important internal condition is the temperature of the body. If the temperature is not stable, the cells cannot work properly. Ideal Body Temperature The ideal temperature for your body is 37ºC. If body temperature rises above 40ºC, you get heatstroke. You could die. If body temperature falls below 35ºC, you get hypothermia. You could die. Maintaining Ideal Body Temperature Your body temperature is controlled by a thermostat. This is in the brain. It monitors the temperature of the blood. If the blood temperature gets too high or too low, it sends nerve signals to parts of the body which respond to protect the body. Temperature too high Sweating blood vessels widen body hair flattens metabolic rate gets slower. When the temperature increases, your body responds by an increase in sweating and the hairs on your body go flat. When sweat evaporates, it cools the skin. The skin turns red because the flow of blood increases so that the body can lose heat into the air. Temperature too low no sweat blood vessels narrow body hair stands up shivering metabolic rate gets faster When the temperature decreases your body gets goose-bumps. This is caused by the hairs on the skin being raised up to trap air to insulate the skin. Blood flow also decreases so that the body loses less heat. This is why we turn pale. Shivering movement also helps us keep heat in. These actions continue until the body temperature goes back to normal.

35 35 The Skin The diagram below shows the layers of the skin.

36 36 Homeostasis Part 2 Maintaining Blood Sugar Levels Blood sugar is called Glucose. It is made from carbohydrates in food and absorbed into the blood from the intestines. The body needs glucose for the cells to work properly. Depending on how much carbohydrate you eat, the amount of glucose in the blood keeps changing. However for the body to work properly, the level of glucose in the blood must be kept stable. If there is too much or too little glucose, you can get diabetes. Glucose levels are controlled by a hormone called Insulin. Insulin is produced in the Pancreas. Glucose levels too high If the glucose level is too high, the receptors in the pancreas detect this and the pancreas slowly pours insulin into the blood. The insulin lets body cells absorb the extra glucose and store it as glycogen in the liver. This means that the glucose level in the blood goes back down to normal. Glucose levels too low If the glucose level is too low, the receptors in the pancreas detect this and the pancreas secretes a hormone called glucagon. The glucagon allows the liver to release the glucose which it has stored. The blood glucose levels can go back up to normal. Diabetes Diabetes is a condition in which the body cannot control the amount of glucose in the blood. People with Type 1 Diabetes cannot produce insulin, so their blood sugar levels are too high. This is treated by injections of insulin. They must be careful of what they eat so that the insulin injections do not make the blood sugar levels fall too low. People with Type 2 Diabetes also can produce some but not enough insulin. Usually this develops in older people. Often it is caused by obesity. It can sometimes be treated by diet and exercise.