Section 1.pdf

Head to savemyexams.co.uk for more awesome resources YOUR NOTES IGCSE Biology Edexcel...

Head to savemyexams.co.uk for more awesome resources YOUR NOTES IGCSE Biology Edexcel  1. The Nature & Variety of Living Organisms CONTENTS Characteristics of Living Organisms 1.1 Characteristics of Living Organisms 1.2 Common Features: Eukaryotic Organisms 1.3 Common Features: Prokaryotic Organisms 1.4 Pathogens Page 1 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Characteristics of Living Organisms YOUR NOTES  1.1 Characteristics of Living Organisms The Unifying Characteristics of Living Organisms In order for something to be considered 'living', it must fulfil specific criteria that are true of all living organisms These criteria can be remembered using the acronym MRS C GREN Movement Respiration Sensitivity Control Growth Reproduction Excretion Nutrition If something does not carry out all of these life processes, it is either dead or non- living Viruses are a good example of non-living particles/agents Page 2 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Nutrition YOUR NOTES Organisms must obtain food to provide energy  Energy is necessary to carry out life processes e.g. movement, respiration and excretion Nutrition in plants Plants use sunlight, carbon dioxide and water to produce oxygen and glucose in the process of photosynthesis Because plants create their own food for energy, they are described as being autotrophic Nutrition in animals Animals consume other living organisms in order to obtain the energy they require They break down larger complex molecules into simpler molecules through the process of digestion As animals obtain their food from a range of different sources, they are described as being heterotrophic Autotrophs make their own food whereas heterotrophs obtain it from a range of food sources. Page 3 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Exam Tip Sometimes understanding the origin of a word can help us to remember the  meaning, for example:Autotroph comes from: 'auto' = 'self' 'trophic' = 'feeding' Heterotroph comes from: 'hetero' = 'different' 'trophic' = 'feeding' Respiration Respiration is a chemical reaction carried out in all living organisms Energy is released from glucose either in the presence of oxygen (aerobic respiration) or the absence of oxygen (anaerobic respiration) The reactions ultimately result in the production of carbon dioxide and water as waste products Energy is transferred in the form of ATP The equation for aerobic respiration  Exam Tip Make sure not to confuse respiration with gas exchange. Gas exchange involves getting oxygen into the cells and carbon dioxide out. Respiration uses the oxygen supplied from gas exchange to release energy in the form of ATP. Page 4 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Excretion YOUR NOTES Chemical reactions that take place inside living cells are described as metabolic  reactions Metabolic reactions produce waste products, some of which may be toxic These toxic products must be eliminated from the body Excretion is the removal of toxic materials and substances from organisms Excretion in animals Waste products excreted by animals include: Carbon dioxide from respiration Water from respiration and other chemical reactions Urea which contains nitrogen resulting from the breakdown of proteins Excretion in humans, the waste products and organs involved. Excretion in plants Waste products excreted by plants include: Oxygen from photosynthesis Carbon dioxide from respiration Water from respiration and other chemical reactions Page 5 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Excretion in plants, the waste products and the difference between day and night.  Exam Tip Excretion is often confused with egestion. Remember that the waste products removed through excretion have originated from chemical reactions in the cells. However, the waste products produced in egestion are in the form of faeces and originate from the remains of the substances not absorbed during digestion. Page 6 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Response to Surroundings YOUR NOTES The sensitivity of an organism refers to its ability to detect and respond to stimuli  in its surroundings Responding to the environment around them gives an organism the best chances of survival Sensitivity responses in animals In humans, the nervous system provides a complex system of receptors, neurones and effectors which detect and respond to different stimuli using electrical impulses The endocrine system also allows a response to stimuli using chemical messengers, which travel in the blood, called hormones The nervous system and endocrine system allow humans to respond to their environment. Sensitivity responses in plants In plants, responses are controlled by chemicals and are usually much slower Geotropism describes a plants response to gravity which causes the roots to grow down into the soil Phototropism describes a plant's response to light which causes shoots to grow towards sunlight Page 7 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Phototropism and geotropism allow plants to respond to their environment. Movement Movement is an action by an organism causing a change of position or place The movement of an organism from place to place is called locomotion Plants cannot move from place to place but can change their orientation For example, sunflowers track the sun and so change their orientation throughout the day Sunflowers track the sun throughout the day. Page 8 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Control YOUR NOTES Living organisms must control their internal environment in order to keep  conditions within required limits This is called homeostasis Homeostasis in humans Thermoregulation refers to the control of body temperature The optimum human body temperature is 37°C If body temperature increases e.g. during exercise, mechanisms for control will be initiated to return the temperature back to the optimum Mechanisms include sweating or vasodilation Other homeostatic mechanisms in humans include glucoregulation (control of blood glucose levels) and osmoregulation (control of water levels) Thermoregulation is an example of homeostasis required to maintain a body temperature of 37°C. Homeostasis in plants Plants use transpiration to maintain a suitable temperature Water evaporates from the stomata on the underside of the leaf, leading to heat loss Page 9 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Plants maintain an optimum temperature through transpiration Page 10 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Reproduction YOUR NOTES Reproduction is the process that leads to the production of more of the same  kind of organism Reproduction is fundamental to the survival of a population and ultimately, the species There are different types of reproduction: sexual and asexual Sexual Reproduction In this type of reproduction, the male and female gametes fuse together In humans, the male gamete is the sperm and the female gamete is the egg In plants, the male gamete is in the pollen grains and the female gamete is the ovule The DNA of the offspring is composed of both maternal and paternal DNA Sexual reproduction involves the fusing of two gametes to form a zygote that contains DNA from both parents. Asexual reproduction Cells or whole organisms can also reproduce using asexual reproduction Mitosis is an example of asexual reproduction There is only one parent involved so an exact clone is produced The DNA of offspring is identical to parental DNA Page 11 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Plants can reproduce asexually through tubers, budding or runners YOUR NOTES Single-celled organisms such as bacteria or amoeba reproduce asexually  Page 12 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Asexual reproduction in bacteria involves creating exact copies of the parent cell. Growth Growth is defined as a permanent increase in size In animals, an individual grows larger between the zygote and adult stage with changes in proportion or shape In plants, an individual grows larger throughout their whole life with new shoots, leaves, branches etc forming year after year Page 13 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources 1.2 Common Features: Eukaryotic Organisms YOUR NOTES  Common Features of Eukaryotic Organisms: Basics All living organisms can be grouped or 'classified' using a classification system that consists of five kingdoms. These five kingdoms are: Animals Plants Fungi Protoctists Prokaryotes The first four kingdoms in this list (the animals, plants, fungi and protoctists) can actually be grouped together, as they are all eukaryotic organisms (also known as eukaryotes) Animals, plants, fungi and protoctists are all eukaryotes. Eukaryotic organisms can be multicellular or single-celled and are made up of cells that contain a nucleus with a distinct membrane Page 14 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources An animal cell (left) and plant cell (right) as seen under a light microscope. They are YOUR NOTES both eukaryotic cells as they both have a distinct membrane-bound nucleus.  Prokaryotic organisms (also known as prokaryotes) are in a separate kingdom and are different from eukaryotes as they are always single-celled and do not contain a nucleus (instead, the nuclear material of prokaryotic cells is found in the cytoplasm) Bacteria are prokaryotic organisms Prokaryotic cells are substantially smaller than eukaryotic cells Page 15 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Animals YOUR NOTES The main features of animals:  They are multicellular Their cells contain a nucleus with a distinct membrane Their cells do not have cellulose cell walls Their cells do not contain chloroplasts (so they are unable to carry out photosynthesis) They feed on organic substances made by other living things They often store carbohydrates as glycogen They usually have nervous coordination They are able to move from place to place A typical animal cell Page 16 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Cell Structures Found in Both Animal and Plant Cells Table YOUR NOTES  Page 17 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Plants YOUR NOTES The main features of plants:  They are multicellular Their cells contain a nucleus with a distinct membrane Their cells have cell walls made out of cellulose Their cells contain chloroplasts (so they can carry out photosynthesis) They feed by photosynthesis They store carbohydrates as starch or sucrose They do not have nervous coordination A typical plant cell Cell Structures Found Only in Plant Cells Table Page 18 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES   Exam Tip You need to be able to recognise, draw and interpret images of cells, so practice drawing and labelling animal and plant cells as part of your revision. Page 19 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Fungi YOUR NOTES Main features of fungi:  They are usually multicellular but some are single-celled (e.g. yeast) Multicellular fungi are mainly made up of thread-like structures known as hyphae that contain many nuclei and are organised into a network known as a mycelium Their cells contain a nucleus with a distinct membrane Their cells have cell walls made of chitin (chitinous cell walls) Their cells do not contain chloroplasts (so they cannot carry out photosynthesis) They feed by secreting extracellular digestive enzymes (outside the mycelium) onto the food (usually decaying organic matter) and then absorbing the digested molecules. This method of feeding is known as saprotrophic nutrition Some fungi are parasitic and feed on living material Some fungi store carbohydrates as glycogen They do not have nervous coordination Examples of fungi include: moulds, mushrooms, yeasts A typical fungal cell. Page 20 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  The typical structure of a multicellular fungus e.g. Mucor (bread mould). Page 21 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Protoctists YOUR NOTES Main features of protoctists:  The protoctists are a very diverse kingdom of organisms that don't really belong in any of the other eukaryotic kingdoms (animals, plants and fungi) They are mainly microscopic and single-celled but some aggregate (group together) into larger forms, such as colonies or chains of cells that form filaments Their cells contain a nucleus with a distinct membrane Some have features making them more like animal cells e.g. Plasmodium (the protoctist that causes malaria) Some have features, such as cell walls and chloroplasts, making them more like plant cells e.g. green algae, such as Chlorella This means some protoctists photosynthesise and some feed on organic substances made by other living things They do not have nervous coordination Examples of protoctists include: amoeba, Paramecium, Plasmodium, Chlorella Two examples of protoctist cells  Exam Tip You need to be able to recognise, draw and interpret images of cells, so practice drawing and labelling fungal cells and protoctist cells as part of your revision. Page 22 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources 1.3 Common Features: Prokaryotic Organisms YOUR NOTES  Prokaryotes All living organisms can be grouped or ‘classified’ using a classification system that consists of five kingdoms. These five kingdoms are: Animals Plants Fungi Protoctists Prokaryotes The prokaryotes are different from the other four kingdoms (which are all eukaryotes) as prokaryotic organisms are always single-celled and do not contain a nucleus Instead, the nuclear material of prokaryotic cells is found in the cytoplasm Bacteria are prokaryotic organisms Bacteria Bacteria, which have a wide variety of shapes and sizes, all share the following biological characteristics: They are microscopic single-celled organisms They have a cell wall (not made of cellulose), cell membrane, cytoplasm and plasmids They lack a nucleus but contain a circular chromosome of DNA They lack mitochondria and other membrane-bound organelles found in eukaryotic cells Examples of bacteria include: Lactobacillus (a rod-shaped bacterium used in the production of yoghurt from milk) Pneumococcus (a spherical bacterium that acts as the pathogen causing pneumonia) Bacteria feed in different ways: Some bacteria can carry out photosynthesis Most feed on other living or dead organisms (if they feed on dead organic matter then they are known as saprobionts or decomposers) Page 23 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  A typical bacterial cell Prokaryotic Cells Table Page 24 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources 1.4 Pathogens YOUR NOTES  Types of Pathogen A pathogen is any microorganism that causes disease in another organism (e.g. in plants or animals) Many microorganisms are pathogens including: Bacteria Fungi Protoctists Viruses Not all species within these groups (apart from the viruses) are pathogens, as many bacteria, fungi and protoctists are harmless and do not cause disease However, all viruses are pathogenic as they can only exist by living inside the living cells of other organisms (or by using these cells to create more viruses) Pathogenic bacteria Pathogenic bacteria do not always infect the hosts of cells, they can remain within body cavities or spaces M. tuberculosis causes tuberculosis (TB) in humans The bacteria infect the lungs, causing a chronic cough and bloody mucus It is a disease often associated with poor hygiene and sanitation M. bovine in cows can also transmit to humans to cause TB N. meningitidis causes bacterial meningitis in humans Very few bacteria can cross the barrier created by the meninges (the tissue that surrounds the brain and spinal cord) however N. meningitidis crosses this barrier to cause acute inflammation Inflammation of the meninges causes symptoms such as fever, headache, neck stiffness and a characteristic rash Pathogenic fungi Fungal diseases are much more common in plants than animals Cattle ringworm and athletes foot are fungal diseases that exist on the surface of the skin Fungal diseases in plants tend to be much more serious and can threaten entire crops Black Sigatoka is a fungal disease in bananas It spreads through the leaves of the plant, reducing its ability to photosynthesise The lack of photosynthesis causes parts of the leaf to die; producing black streaks Eventually, the whole leaf dies Pathogenic protoctists Plasmodium falciparum is a protist that causes severe forms of malaria in humans The parasite is spread by mosquitoes Infected individuals experience fever, chills and fatigue P. infestans causes the infamous potato blight Page 25 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources The pathogen is unusual as it has some fungal characteristics YOUR NOTES It is transmitted via spores  The first signs of potato blight are small, dark brown marks on the leaves which quickly increase in size and number The protist destroys potato and tomato crops leaving them completely inedible Page 26 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Viruses YOUR NOTES Viruses are not usually included in the classification of living organisms as they  are not considered to be alive This is due to the fact that viruses do not carry out the 8 life processes for themselves In fact, the only life process they seem to display is reproduction but even to carry out this process they must take over a host cell’s metabolic pathways in order to make multiple copies of themselves Viruses, which have a wide variety of shapes and sizes, all share the following biological characteristics: They are small particles (always smaller than bacteria) They are parasitic and can only reproduce inside living cells They infect every type of living organism They have no cellular structure but have a protein coat and contain one type of nucleic acid, either DNA or RNA Structure of a typical virus Examples of viruses include: Page 27 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources The tobacco mosaic virus (TMV) causes discolouring of the leaves on tobacco YOUR NOTES plants by preventing the formation of chloroplasts  The HIV virus causes AIDS The influenza virus causes the ‘flu’ Tobacco mosaic virus Tobacco mosaic virus (TMV) was the first virus to be isolated by scientists It is a widespread plant pathogen that infects about 150 species of plants including tomato plants and cucumbers TMV Table HIV HIV (Human Immunodeficiency Virus) is a virus that can eventually lead to Acquired Immunodeficiency Syndrome (AIDS) HIV Table Page 28 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Influenza virus Three different influenza viruses infect humans to cause the flu Influenza A, influenza B and influenza C infect the cells that line the airways They cause a high temperature, body aches and fatigue Influenza A is the virus that causes the most cases of flu globally Page 29 of 29 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers