GCSE Revision Booklet Biology Unit B1 Influences of life

Transcription

1 GCSE Revision Booklet Biology Unit B1 Influences of life

2 Classification, Inheritance and variation Classification Each different organism (living thing) has a unique classification that gives it a binomial (two word) name. E.g. dogs are called Canis familiaris in the binomial system. This system is divided into 7 divisions in a rank order they are: Kingdom phylum class order family genus species So dogs have the following classification: Kingdom Animalia (Animal) Phylum Chordata (vertebrate) these are animals with a spine Class mammalia (mammal) Order Carnivora (Carnivores) Family Canidae Genus Canis Species familiaris Use this phrase to help your remember the order Keep Plates Clean Or Family Gets Sick. The five kingdoms are: Animalia all animals e.g. jellyfish, worms, chimpanzees Plantae all green plants e.g. ferns, moss, conifers and roses Fungi any fungus big or small e.g. moulds, yeast, mushrooms Protoctista only one cell but, with a nucleus e.g. amoeba & paramecium Prokaryotes only one cell but with no nucleus e.g. bacteria & blue-green algae Scientists do not classify a virus as a living thing because they do not show all seven processes for life. The five chordate (vertebrate) groups are: Fish gills, fins, wet scales, external fertilisation Amphibian smooth skin, lungs or gills, external fertilsiation Reptile dry scaly skin, eggs with hard shells, internal fertilisation Bird wings, feathers, eggs with hard shells, internal fertilisation Mammal hair/fur on body, give birth to live young, feed young on milk, internal fertilisation

3 A Species is a group of similar organisms that can interbreed and produce fertile offspring. A Hybrid is the infertile offspring that occurs, when two different species breed/reproduce. Evolution Charles Darwin ( ) proposed the theory of evolution that scientists accept today. Evolution is the slow, continual change of organisms over a very long time. All living things on the Earth have developed from the first simple life forms that arrived 3,000,000,000 years ago. One of the effects of evolution is that species will become better adapted to their environment. If these species don t adapt they may become extinct due to being unable to deal with any of these factors: 1) increased competition, 2) changes in the environment, 3) new diseases, 4) new predators My key observations: variation in any population of organisms there will be some differences over-production many organisms produce more offspring than survive to adulthood struggle for existence there is competition of survival and resources between the organisms. survival those with helpful characteristics are more likely to survive to breed useful characteristics inherited by the offspring gradual change of the species over a period of time as useful characteristics are passed to offspring. Darwin s theory of Natural Selection 1) Each species shows variation: 2) There is competition within each species for food, living space, water, mates etc.

4 3) The better adapted members of these species, are more likely to survive Survival of the Fittest and reproduce. 4) These survivors will pass on their better genes to their offspring who will also show this beneficial variation.

5 Evidence for Darwins theory Fossil records despite some gaps show how much (or how little) different organisms have changed since life developed on Earth. Antibiotic-resistant bacteria bacteria reproduce rapidly and can evolve in a short time, if the mutation (such as antibiotic resistance) is an advantage, they are more likely to survive and evolve further. DNA Scientists can now examine the DNA of different species and see how closely related they are to each other, e.g. Chimpanzees and humans share 96% of our DNA Adaptation Every organism has certain features that allow it to survive in its habitat so the organism is adapted to its habitat, organisms living in different environments will have different adaptations. You need to be able to explain how organisms are adapted to survive in different habitat extremes. You give the feature and then explain how it helps. Artic or Antartic Environment Animals Thick layer of fat and fur- insulation against the cold Small surface area to volume ratio to minimise heat loss A greasy coat, which sheds water after swimming. White fur to camouflage. Large feet to prevent sinking in the ground Plants Grow close to the ground stop it being blown by the wind Have very small leaves prevent water loss

6 Deep Sea Hydrothermal Vents Thick layer of bacteria to protect it from predators. Makes a paper like tube to hide it from predators

7 Variation Variation means differences within a species Some of this variation is due to our parents inherited variation, but some of it is due to our upbringing and the environment in which we live Environmental variation Inheritance Only Environmental Only Both Inherited and Environmental Blood Group Scars Height Natural Eye colour Injuries Weight Natural Hair Colour Some features in organisms show either continuous or discontinuous variation. Continuous variation Is a characteristic in any species that changes gradually over a range of values. Examples include: height, weight, foot length etc - So height ranges from the smallest person in the world to the largest person and all the possible values in between. A graph showing continuous variation will look like this (it is known as a bell shaped curve or normal distribution) if you have data from a large sample size. Discontinuous variation A characteristic of any species with only a limited number of possible values. Examples include: gender, blood group, eye colour So human blood only has four possible values A, B, AB, or O) A discontinuous graph looks like the one below, it will not form a bell shape.

8 Inheritance All cells in the body (except the red blood cells) contain a nucleus which controls the cell. Chromosome Chromosomes are made from long DNA molecules The nucleus contains chromosomes gene A gene is a short section of DNA Every persons DNA is unique (except for identical twins), this is why DNA can be used to identify people. Alleles Different forms of the same gene are called alleles and they can be dominant or recessive the characteristics controlled by a dominant allele develops if the allele is present on one or both chromosomes in a pair the characteristic controlled by a recessive allele develops only if the allele is present on both chromosomes in a pair e.g. the genes controlling the hairline growth on a human forehead has a recessive allele for a straight hairline and a dominant allele for a widows peak hairline. In genetic diagrams a dominant allele will always be shown by a capital letter, while the recessive allele is shown as a lower-case letter.

9 So if the genotype is WW or Ww the person will have a widows peak hairline, but if the genotype is ww the person has a straight hairline. However the Ww genotype displays a widows peak hairline, but they are carrying the allele for a straight hairline. WW ww W W w w Ww Ww Ww Ww Note: WW is described as being homozygous for the dominant allele ww is described as being homozygous for the recessive allele Ww is described as being heterozygous Cystic fibrosis Cystic fibrosis (Cf) is caused by a recessive allele. People with CF produce abnormally thick sticky mucus in their lungs and airways, so sufferers are more likely to get respiratory diseases. If a child has CF then both parents must either have CF or be carriers of the CF allele Mother father F f F FF Ff f Ff ff. Mother father F F F FF FF f Ff Ff

10 Sicke cell disease Sickle cell disease is another recessive conditions so the genetic crosses for it will be similar to the ones above for Cystic fibrosis. In Sickle cell anemia the red blood cells become misshapen and can stick together which can block blood vessels. Sickle cell disease sufferers can become very tired and quickly get out of breath. If the sickle cells block a blood vessel, this can be fatal. Responses to a changing environment Homeostasis Homeostasis means controlling internal conditions using the nervous system and hormones. CO 2 Urea Waste products that need to be removed + how Produced by respiration, removed via lungs Produced by liver breaking down amino acids, removed by kidneys and transferred to bladder Temperature Ion content Water content Internal conditions that need controlling + how Increased by shivering, lost by sweating Increased by eating, lost by sweating + urine Increased by drinking, lost by sweating + urine

11 Blood Glucose Increased and decreased by hormones Controlling water content (Osmoregulation) Water loss is controlled by water loss from the lungs, when we exhale (breathe out) the skin by sweating the body, in urine produced by the kidneys Osmoreceptors in pituitary Less ADH is released In the kidneys Water Increases Normal Water Level Water Increases Water Decreases ADH is released In the kidneys Osmoreceptors in pituitary Controlling the Ions (salts) in the body This is controlled to protect cells by avoiding too much water entering or leaving them. Ion content is controlled by loss of ions from: the skin by sweating the body, in urine produced by the kidneys

12 Controlling body temperature (Thermoregulation) Human enzymes usually work best at 37 C, this is our core body temperature. High temperatures can cause dehydration, heat stroke and death if untreated Low temperatures can cause hypothermia and death if untreated. The brain monitors the body s temperature, if you are too hot or too cold it sends nerve impulses to the skin. Hairs on the skin are controlled by the erector muscle, when it contracts the hairs stand end (goosepimples) trapping warm air near the skin, if it is too hot the erector muscle relaxes so the hair can lie flat. Sweating cools you down. When you are too hot, sweat is secreted onto the surface of hot skin by glands underneath the skin. The sweat evaporates using the heat energy from your body, which takes the heat away from the skin and cools you down. Blood vessels near the surface of the skin can swell (vasodilation) which cause more blood to be passed to the surface of the skin and the heat is radiated away, or they can get smaller (vasoconstriction) this prevents heat loss as less blood goes to the surface of the skin so less heat gets radiated out.

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14 Hormones Glands in the hypothalmus section of the brain Thyroid gland Adrenal glands Pancreas Ovaries (in females) Testes (in males) Gland Hormone Target organs Ovary Oestrogen Overies, uterus Ovary Progesterone Uterus Pancreas Insulin & Glucogon Liver Testes Testosterone Male reproductive organs Insulin released by the pancreas Liver converts Glucose to glycogen Glucose Increases Glucose Decreases Normal Blood Glucose Level Glucose Increases Glucose Decreases Liver converts Glycogen to glucose Glucogon released by the pancreas

15 Diabetes Diabetes is a disorder in which the blood glucose levels can be too high, there are three main types of diabetes: Type 1 diabetes is caused by a lack of insulin due to either a genetic disorder or as a side effect of a viral infection. The diabetes is controlled by monitoring the diet Injecting insulin People with type 1 diabetes have to monitor their blood sugar levels throughout the day as the level of their activity and diet changes, which will affect the amount of insulin the will need to take in. Type 2 diabetes is caused by a person becoming resistant to insulin due to them being very overweight. It can be controlled by diet and exercise. The number of people who suffer from type 2 diabetes is rising due to increasing obesity. A person in considered obese if they have a body mass index (BMI) of over 30, if they have a BMI of 20 or under they are considered to be underweight. The formula for BMI is: weight in kilorams (kg) height in metres 2 (m 2 ) It is important to remember that the BMI calculation is just a guide and it has many flaws, people who have good muscle tone and who are not particularly tall may have a BMI of over 30 despite having a very healthy lifestyle. Plant hormones A tropism is a growth in response to a stimulus. Auxin is a plant hormone that is made in the stem tips and roots, which controls the direction of growth. Plant hormones are used in weedkillers, rooting powder and to control fruit ripening. Response Part of plant Direction of growth Advantage Positive phototropism Stem tip Growth towards light To get maximum light for photosynthesis Negative phototropism Root tip Growth away from light Less chance of drying out Positive Root tip Towards gravity More chance of finding geotropism Negative geotropism moisture Stem tip Away from gravity More chance of finding light. Controlling the direction of growth A plant grows towards the light because light destroys the auxin in that side of the stem, so growth on that side of the plant slows down. On the shaded side the plant has more auxin, so growth on that side speeds up. This results in the plant bending towards the light to maximise photosynthesis.

16 A = The tips have been cut off removing the auxin, so phototropism can t happen. B = The tinfoil caps stop the light destroying the auxin, so it remains evenly distributed and the shoots grow straight up. C = The light destroys the auxin on the that side of the plant, so more auxin is on the shaded side causing the cells to elongate, so the shoot bends towards the light.