HUGE PACK: IGCSE Flashcards
functions of all living organisms:
M ovement: can change position
R eproduction: can have offspring either sexually or asexually
S ensitivity: can detect stimuli, such as light, and respond to them
C ontrol: can control their internal environment (homeostasis)
G rowth: can increase mass
R espiration: can produce energy either aerobically or anaerobically
E exretion: can remove toxic waste produced, produced by reactions in the body
N utrition: can absorb nutrients in order to use them for growth and repair
eukaryotic organisms:
-> eukaryotes are organisms that have a nucleus and organelles that are found within a plasma membrame
-plants
-animals
-fungi
-protoctists
plants: characteristics
e.g. cereals (such as maize) or herbaceous legume (such as peas)
-multicellular organisms
-cells contain chlorplasts which is the site of photosynthesis: chlorophyll pigments within the chloroplast structure absorb light from the Sun
-they store carbohydrates as starch or sucrose
animals: characteristics
e.g. mammals (such as humans) and insects (such as flies)
-multicellular organsisms
-cannot photosynthesise
-don’t have cell walls
-most have nervous systems in order to coordinate movement
-store carbohydrates as glycogen
fungi: characteristics
e.g. yeast (single-celled) and mucor (has the typical hyphal structure)
-some are single-celled
-others have a body organised into a mycelium of thread-like structures called hyphae which have many nuclei
-cell walls are made of chitin
-feed by extracellular secretion of digestive enzymes which break it down into smaller pieced, which can then be absorbed (saprotrophic nutrition)
-may store carbohydrates as glycogen
protoctists: characteristics
e.g. amoeba (animal-cell like + live in pond water) and chlorella (plant-cell like)
-they are microscopic and single-celled
-some have features like animal cells
-others are more like plants and have chloroplasts
prokaryotic organisms:
-> prokaryotes do not have a nucleus or membrame-bound organelles
-bacteria
bacteria: characteristics
e.g. lactobacillus bulgaris (rod-shaped bacterium used to make yoghurt) and pneumococcus (spherical bacterium that causes pneumonia)
-single-celled and very small
-have a cell wall, cell membrame, cytoplasm and plasmids
-lack a nucleus but have circular choromosomes of DNA
-some can carry out photosynthesis but they mainly eat off of other organisms, either dead or alive
pathogens:
-> pathogens are disease-causing organisms and can be fungi, bacteria, protoctists or viruses
viruses characteristics:
e.g. tobacco mosaic virus which prevents chloroplast formation, influenza virus, HIV virus leading to AIDS
-viruses are small particles (much smaller than bacteria)- not living organisms
-they are parasitics -> can only reproduce within living cells, can infect every type of living organisms, hijacks the cell mechanisms to create millions of copies of itself and then spreafs within the host by cell bursting
-they come in a wide variety of shapes and sizes
-do not have a cellular structure but have one type of nucleic acid (either DNA or RNA) and a protein coat
pathogens: other pathogens
-protoctists: plasmodium that causes malaria
-bacteria: pneumococcus which causes pneumonia
-viruses: influenza virus (which causes the ‘flu’) and HIV (which causes AIDS)
-fungi: causes athlete’s foot but can be treated with fungicides
levels of organisation: organelles, cells, tissues, organs and organ systems
-organelles: specialised subcellular structures found within living cells
-cells: basic structural unit of a living organism
-tissues: group of cells with similar structures, working together to perform the same function
-organs: group of tissues, working together to perform specific functions
-organ system: group of organs with similar functions, working together to perform body functions
an examples of this would be the respiratory system organ system, containing the lungs (organ), which is made up of epithelial tissue consisting of epithelial cells
subcellular structures: found in plant and animal cells
-nucleus: contains the genetic material which codes for a particular protein, enclosed in a nuclear membrame
-cytoplasm: liquid substance in which chemical reactions occur, contain enzymes (biological catalysts, i.e. proteins that speed up the rate of reaction), organelles are found in it
-cell membrame: contain receptor molecules to identify and selectively control what enters and leaves the cell
-mitochondria: where aerobic respiration reactions occur, providing energy for the cell
-ribosomes: where protein synthesis occurs, found on a structure called the rough endoplasmic reticulum
subcellular structures: found only in plants
-chloroplasts: where photosynthesis takes place providing food the plant, contains chlorophyll pigment (which makes it green) which harvests the light needed for photosynthesis
-permanent vacoule: contains cell sap, found within the cyctoplasm, improves cell’s rigidity
-cell wall: made from cellulose, provides strength to the cell
biological molecules: carbohydrates
-they are made of carbon, oxygen and hydrogen
-they are polymers that break down into simple sugars
biological molecules: proteins
-they are made of carbon, oxygen, hydrogen, sulfur, nitrogen and phosphorus
-they are polymers that are broken down into its monomers: amino acids
biological molecules: lipids
-lipids (fats and oils) are made of carbon, oxygen and hydrogen
-they are large polymers that are broken down into 3 fatty acids molecules and a glycerol molecule
practical: investigate food samples for the presence of glucose, starch, protein and fat - Test for glucose
1) add the sample solution into a test tube
2) add drops of Benedict’s solution into the test tube
3) heat in a water bath at 60-70ºC for 5 minutes
4) take test tube out and record the colour
-if glucose is present the solution will turn brick red
-if glucose is not present that the solution will remain blue
practical: investigate food samples for the presence of glucose, starch, protein and fat - Test for starch
1) pipette the sample solution into wells or on a tile
2) add drops of iodine solution and leave for 1 minute
3) record any colour change
-if starch is present the solution will turn blue-black
-if starch is not present the solution will remain brown
practical: investigate food samples for the presence of glucose, starch, protein and fat - Test for protein
1) add the sample solution into a test tube
2) add drops of Biuret solution into the test tube
3) leave for 1 minute and then record the colours
-if protein is present the solution will turn purple
-if protein is not present that the solution will remain blue
practical: investigate food samples for the presence of glucose, starch, protein and fat - Test for fat
1) add 2cm^3 of ethanol to the test solution
2) add 2cm^3 of distilled water
3) leave for 3 minutes and then record the colour
-if fat is present a milky white emulsion will form
-if fat is not present that the solution will remain colourless
enzymes:
-> enzymes are biological catalysts (a substance that increases the rate of reaction without being used up)
-they are protein molecules and the shape of the enzyme is vital to its function
-this is because each enzyme has its own uniquely shaped active site where the substrate binds, a simplified way to look at how they work is the Lock and Key Hypothesis:
-the shape of the substrate is complementary to the shape of the active site (enzyme specificity), so when they bond it forms an ezyme-substrate complex
-once bound, the reaction takes place and the products are released from the surface of the enzyme
enzymes: effect of temperature
-the optinum is around 37ºC (body temperature)
-the rate of reaction increases with an increase in temperature to up to this optimum, but above this temperature it rapidly decreases and eventually the reaction stops
-when the temperature becomes too hot, the bonds in the structure will break
-this changes the shape of the active site, so the substrate can no longer fit in
-the enzyme is said to be denatured and can no longer work
practical: investigate how enzyme activity can be affected by changes in temperature
1) starch solution is heated to set temperature
2) amylase is added
3) iodine is added to each well after a minute
4) measure the time it takes until the iodine stops turning blue-black (this means that starch is not present as amylase has broken the starch down into glucose)
5) repeat the test with different temperature
enzymes: effect of pH
-the optinum pH for most enzymes is 7, but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH
-if the pH is too high or too low, the forces that hold the amino acid chains that make up the protein will be affected
-this will change the shape of the active site, so the subtrate can no longer fit in
-the enzyme is said to be denatured and can no longer work
diffusion:
-> diffusion is the spreading out of the particles resulting in a net movement from an area of higher concentration to an area of lower concentration
-it is a passive process as no energy is required
-the molecules have to be small in order to be able to move across, for example oxygen, glucose, amino acids and water, but larger molecules such as starch and proteins cannot
diffusion: examples
-single-celled organisms can use diffusion to transport molecules into their body ffrom the air -> this is because they have a relatively large surface area to volume ration. Due to their low metabolic demands, diffusion across the surface of the organism is sufficient enough to meet its needs
-in multicellular organisms the surface area to volume ratio is small so they cannot rely on diffusion alone. Instead, surfaces and organ systems have a number of adaptations that allows molecules to be transported in and out of cells. Examples include alevioli in the lungs, vili in the small intestines and root hair cells in plants
factors affecting rate of movement: concentration gradient
-the greater the difference in concentration, the faster the rate of diffusion
-this is because more particles are randomly moving down the gradient than are moving against it
factors affecting rate of movement: temperature
-the greater the temperature, the greater the movement particles, resulting in more collisions and therefore a faster rate of diffusion
factors affecting rate of movement: surface area:volume
-the greater the surface area, the more space for particles to move through, resulting in a faster rate of diffusion
factors affecting rate of movement: distance
-the further the particles have to travel the longer it will take
osmosis:
-> osmosis is the movement of water molecules from a more concentrated solution to a less concentrated solution through a partially permeable membrame
-a dilute solution of sugar has a high concentration of water (and therefore a high water potential). A concentrated solution of sugar has low concentration of water (and therefore low water potential). Water moves from a dilute solution to a concentrated solution because it moves from an area of high water potential-down a concentration gradient
-it is passive, as it does not use energy
important terms: isotonic, hypertonic & hypotonic
-isotonic: if the concentration of sugar in an external solution is the same as the internal, there will be no movement and the solution is said to be isotonic to the cell
-hypertonic: if the concentration of sugar in external solution is higher than the internal, water moves out, and the solution is said to be hypertonic to the cell
-hypotonic: if the concentration of sugar in an external solution is lower than the internal, water moves in, and the solution is said to be hypotonic to the cell
osmosis: examples
-osmosis in animals: if the external solution is more dilute (higher water potential), it will move into animal cells causing them to burst + if the external solution is more concentrated (lower water potential), excess water will leave the cell causing it to become shrivelled
-osmosis in plants: if the external solution is more dilute, water will move into the cell and into the vacuole, causing it to swell, resulting in pressure called tugor (essential in keeping the leaves and stems of plants rigid) + if the external solution is less dilute, water will move out of the cell and they will become soft. Evetually the cell membrame will move away from the cell wall (called plasmolysis) and it will die
active transport:
-> active transport is the movement of particles from an area of lower concentration to an area of higher concentration, i.e. against the concentration gradient
-this requires energy from respiration as it is working against the gradient, which is why it is called active
active transport: examples
-in root hair cells: they take up water and mineral ions (for healthy growth) from the soil + minerals ions are usually in higher concentrations in the cells, meaning diffusion cannot take place + this requires energy from respiration to work
-in the gut: substances such as glucose and amino acids from your food have to move from your gut into your bloodstream + sometime there can be a lower concentration of sugar molecules in the gut than the blood, meaning diffusion cannot take place + active transport is required to move the sugar to the blood against its concentration gradient
practical: investigate diffusion in non-living systems
1) cut a 1cm^3 cube of agar made of sodium hydroxide and phenolphthalein indicator
2) place cube in solution of hydrochloric acid
3) remove the cube and wash with water to stop further reaction
4) cut the cube in half and measure the distance that the acid has caused agar to become colourless from outside inwards
5) repeat the experiment two more times and calculate the mean
6) repeat with different concentrations of hydrochloric acid
practical: investigating osmosis in potatoes
1) place different surcrose solutions including 0% for a control, in different boiling tubes
2) dry potato strips on a paper towel and measure the masses
3) place each potato strip into each surcrose solution for 20 minutes and record how the mass changed
4) repeat tests at each solution several times with potato strips of similar masses
photosynthesis:
-> photosynthesis is the process of making glucose from sunlight in the leaves of the plant. It is an endothermic reaction in which light energy is converted into chemical energy within the chloroplasts
carbon dioxide + water -(light)> glucose + oxygen
6CO2 + 6H2O -> C6H12O6 + 6O2
factors affecting photosynthesis: temperature
-with an increase intemperature, the rate of photosynthesis increases
-however, as the reaction is controlled by enzymes, this trend only continues up to a certain temperature until the enzymes begin to denature and the rate of reaction decreases
factors affecting photosynthesis: light intensity
-for most plants, the higher the light intensity, the rate of photosynthesis increases, i.e. it is inversely proportional to the square of the distance: light intensity ∝ 1/distance^2
-e.g. this means that if a lamp is 2 metres away from a plant, then light intensity of the lamp is a 1/4 of its original value -> 1/2^2 = 1/4
factors affecting photosynthesis: carbon dioxide concentration
-carbon dioxide is also needed to make glucose
-as the concentration of carbon dioxide increases, the rate of reaction increases
leaf structures:
-waxy cuticle: helps to reduce water loss by evaporation and is a protective layer found at the top of the leaf
-upper epidermis: very thin and transparent in order to let light into the palisade mesophyll
-palisade mesophyll: contain lots of chloroplasts so that photosynthesis can happen rapidly
-spongy mesophyll: have lots of air space to allow gases to diffuse in and out of cells faster, as it increases the surface area to volume ratio
-lower epidermis: contains guard cells and stomata (gaps)
-guard cell: kidney-shaped cells that open and close the stomata by absorbing or losing water. When lots of water is available, the cells fill and open stomata
-stomata: where gas exchange and loss of water by evaporation takes place-opens during the day and closes at night
mineral ions:
-magnesium: required for chlorophyll production + defiency: causes leaves to turn yellow
-nitrate: required to produce amino acids + defiency: causes stunted growth and turns leaves yellow
practical: investigating photosynthesis
-use water plants, such as Elodea which releases bubbles of oxygen when photosynthesising
-a lamp with an LED bulb is set up beside the beaker of water containing the water plant. An LED is best as it will not raise the temperature of the water
-sodium hydrogen carbonate (NaHCO3) is added to the water to supply carbon dioxide
-this can set up can be used to investigate the evolution of oxygen from a water plant
practical: investigating the effect of light intensity
1) place pondweed in water and set up a desk lamp next to alongside a ruler so that you can measure the distance between the light and the beaker
2) move the lamp away by 10 cm
3) leave for 5 minutes to allow for the pondweed to adapt
4) cound the number of bubbles given off in 1 minute and record
5) repeat steps 2-4
practical: investigating the effect of carbon dioxide
-complete the experiment of light intensity but instead of testing the variable of light intensity by using a lamp, use different concentrations of sodium hydrogen carbonate solution, whilst keeping the other variables the same
practical: investigating starch production
1) cover half of a small leaf with foil
2) place the plant on a windowsill for 48 hours so that light can reach it
3) put the leaf in a boiling water to kill and preserve it
4) put the leaf in a boiling tube containing hot ethanol for 10 minutes (this removes the chlorophyll pigment)
5) dip the leaf in boiling water to soften it
6) put leaf in a Petri dish and cover with iodine solution
6) the covered half of the leaf will remain orange-brown, whereas the exposed half will change to blue-black (as iodine solution changes colour in the presence of starch, as photosynthesis turned the glucose into starch for storage)
practical: experiment provide photosynthesis requires chlorophyll
-repeat the experiment of starch production but with a variegated leaf
-variegated plants are white and green and only contain chlorophyll in the green parts
-therefore only the green areas of the plant will test positive for starch (i.e. turn blue-black) as a result of photosynthesis occuring
-the white areas that do not contain chlorophyll remain an orange-brown colour
a balanced diet: source and function
-carbohydrates: bread, cereal, pasta, rice, potatoes -> a high energy source
-proteins: meat, fish, eggs, pulses -> for growth and repair
-lipids: butter, oil, nutes -> a high energy source and for insulation
-dietary fibres: vegetables, bran -> to provide rouphage to keep food moving through gut-defiency causes constipation
-vitamin A: carrots, green vegatbles -> needed for vision, especially in the dark, and for growth
-vitamin C: citrus fruits, broccoli, peppers -> helps to absorb iron
-vitamin D: margarine, oily fish -> helps to absorb calcium
-calcium: milk -> for bone and teeth strength-deficiency can cause rickets (curving of bones)
-iron: red meat -> needed for haemoglobin-deficiency can cause anaemia
-water: water, juice, milk -> needed for cell reactions to take place
factors affecting energy requirements:
-age: energy requirements generally increases as we approach adulthood + energy needs of adults go down as they age
-activity levels: if you are more active then you will need more energy for movement
-pregnancy: energy requirements will increase in order to support growth of the foetus + energy needs also increase due to the extra mass of the baby
human alimentary canal: mouth + oesophagus
-> the alimentary canal is the passage food moves through once it has been eaten
mouth:
-mechanical digestion: teeth break up large food pieces into smaller pieces with larger surface area to volume ratio (food bolus)
-chemical digestion: amylase breaks down starch into glucose
-salivary glands produce saliva to lubricate the food bolus so it can be swallowed easily
oesophagus:
-tube from the mouth to the stomach
-food bolus moves down due to unidirectional wave-like contractions (peristalsis) created by circular muscles and longitudinal muscles that create a squeezing action
human alimentary canal: pancreas + stomach
pancreas:
-produces carbohydrase, protease and lipase enzymes
-secretes enzymes into the stomach and small intestine
stomach:
-gastric juice is released from stomach lining when it detects food in the stomach
-gastric juice is made of: pepisin -> enzyme breaking down proteins + hydrochloric acid -> makes stomach acidic in order for pepsin to work and to kill any ingested bacteria
-peristalsis also occurs here
-the digested food is now called chyme
small intestine: duodenum + ileum
duodenum:
-the first part of the small intestine
-carbohydrases, proteases and lipases digest food here
-bile is released into the duodenum: bile is produced in the liver and stored in the gallbladder, it has 2 roles:
1) it is an alkaline to neutralise the hydrochloric acid which comes from the stomach. The enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach
2) it breaks down large drops of fat into smaller ones (emulsifies it). The larger surface area allows lipase to chemically break down the lipid into glycerol and fatty acids faster
-peristalsis also occurs here
ileum:
-lined with vili (finger-like projections) to maximise absorption of digested soluble molecules into blood
-vili have a thin lining, a large network of capillaries and have a large surface area
large intestine:
-water is absorbed here, to produce faeces
-faeces is stored in the rectum and then removed through the anus
digestive enzymes:
carbohydrates (starch):
-broken down by carbohydrases
-starch -> maltose by amylase
-maltose -> glucose by maltase
proteins:
-broken down by proteases in the stomach and small intestine
-proteins -> amino acids
lipids:
-broken down by lipases
-lipids -> glycerol + 3 fatty acids
respiration:
-> respiration occurs in every cell in the body of all living things to supply ATP to cells
-cellular respiration is an exothermic reaction
-two types: aerobic and anaerobic
aerobic respiration:
-this uses oxygen
-it yields the most energy
-most of the reactions that make up aerobic respiration occur in the mitochondria
glucose + oxygen -> carbon dioxide + water
C6H12O6 + O2 -> CO2 + H2O
anaerobic respiration:
-occurs when there is not enough oxygen
-it does not yield as much energy as aerobic respiration
-it is only used as a last resort, for example during a sprint where it is difficult to breathe in enough oxygen
-the oxidation of glucose is complete
in animals:
glucose (C6H12O6) —> Lactic acid
in plants and yeast cells it is called fermentation:
glucose (C6H12O6) —> ethanol + carbon dioxide (CO2)
-this reaction is used to make bread and alcoholic drinks
practical: investigate the evolution of carbon dioxide from respiring seeds or other suitable living organisms
1) connect a capillary tube from the air into a flask containing sodium hydroxide, which will also absorb carbon dioxide
2) connect this flask with a capillary tube to another flask containing hydrogen carbonate indicator (which is red at neutral pH and yellow at low pH, i.e. when carbon dioxide is present)
3) connect the second flask to a third flask containing either germinating seeds or respiring animals, such as worms
4) connect the third flask to another flask containing hydrogen carbonate indicator, such as in step 2
-the sodium hydroxide solution in the first flask will absorb carbon dioxide from the air, which will turn the second flask red, as it will have neutral pH. However, the respiring organism will produce carbon dioxide and will therefore turn the indicator yellow
practical: investigate the evolution of heat from respiring seeds or other suitable living
1) use 2 vacuum flasks, one containing living germinating seeds and the other containing dead or boiled seeds (as a control)
2) put a thermometer wrapped in cotton wool (to prevent heat from escaping) to measure temperature
3) measure initial temperature
4) leave seeds for a few days and then measure end temperature
-the live germinating seeds will release a heat due to aerobic respiration and so the temperature will increase
