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SB1 - Key concepts in biology (SB1b - Plant and animal cells (A cell with…
SB1 - Key concepts in biology
SB1a - Microscopes
To work out a microscope's magnification, multiply the magnifications of its two lenses together
SB1b - Plant and animal cells
A cell with a nucleus is described as eukaryotic
Cell membrane - controls what enters and leaves the cell and separates one cell from another
Cytoplasm - contains a watery jelly and is where most of the cell's activities occur
Mitochondria - jelly-bean shaped structures where aerobic respiration occurs
Nucleus - Controls the cell and its activities, inside are chromosomes which contain DNA
Ribosomes - make new proteins for a cell
Cell wall - made of cellulose and supports and protects the cell
Chloroplasts - contain chlorophyll, which traps energy transferred from the Sun, which is the used for photosynthesis
Vacuole - stores cell sap and helps to keep the cell firm and rigid
Animal cells have: a cell membrane, cytoplasm, mitochondria a nucleus and ribosomes
Plant cells have: a nucleus, a cell wall, cytoplasm, a cell membrane, chloroplasts and a vacuole
SB1c - Specialised cells
Specialised cells have a specific function and there are about 200 different types of specialised cells in humans
Digestion
The cells that line the small intestine absorb small food molecules produced by digestion. They are adapted by having membranes with many tiny folds (microvilli). These adaptations increase the surface area of the cell, the more area for molecules to be absorbed, the faster absorption happens.
Cells in the pancreas make enzymes needed to digest certain foods in the small intestine and they are proteins so they have lots of ribosomes
The wall of the small intestine has muscles to squeeze food along. The muscle cells require a lot of energy and are adapted by having many mitochondria
Reproduction
During sexual reproduction, two gametes (haploid specialised cells) fuse to create a cell that develops into an embryo
Gametes contain one copy of each chromosome, so the cell produced by fertilisation has two copies
Female gamete - egg cell
Cell membrane: fuses with sperm cell membrane and hardens after fertilisation, to stop other sperm cells entering
Cytoplasm: packed with nutrients, to supply the fertilised egg cell with energy and raw materials for the growth and development of the embryo
Jelly coat: protects the egg cell and also hardens after fertilisation to prevent other sperm cells entering the cell
Male gamete - sperm cell
Shape: streamlined for fast swimming
Acrosome (at the tip of the head): contains enzymes that break down the substances in the egg cell's jelly coat, to allow the sperm to burrow inside
Mitochondria: large amount arranged in a spiral around the top of the tail, to release lots of energy to power the tail
Tail: waves from side to side, allowing the sperm cell to swim
Oviducts: where fertilisation occurs in the female reproductive system
Cells in the lining of the oviduct transport egg cells towards the uterus, using cilia, which wave from side to side to sweep substances along
Cells that line structures in the body are called epithelial cells, and epithelial cells with cilia are called ciliated epithelial cells
SB1d - Inside bacteria
Bacteria are prokaryotic, which means that their cells do not have nuclei or chromosomes, but the cytoplasm contains one large loop of chromosomal DNA, which controls most of the cell's activities
There are smaller loops called plasmid DNA, which controls a few of the cell's activities
Prokaryotic cells do not have mitochondria or chloroplasts
Bacteria sub-cellular structures:
Flagellum: not covered in a membrane and not all bacteria have them, but some have many flagellum
Slime coat: for protection - not all bacteria have this
Flexible cell wall: for support - not made out of cellulose
Cell membrane
Ribosomes
Chromosomal DNA
Cytoplasm: contains ribosomes, which are smaller than eukaryotic ribosomes
SB1e - Enzymes and nutrition
Bacteria release digestive enzymes into their environments and the absorb digested food into their cells
In humans, digestive enzymes turn the large molecules in our food into smaller subunits they are made of, so that they can be small enough to be absorbed y the small intestine
Protein, broken down by protease to form amino acids
Starch, broken down by amylase to form glucose
Lipids, broken down by lipase to form fatty acids and glycerol
Monomers are the smaller molecules that make up polymers
Enzymes are biological catalysts because they increase the rate of reactions
SB1f - Testing foods
Reducing sugars = Benedict's Reagent
Add Benedict's reagent to a sample and heat in a 75degreesC water bath. If the test is positive it will form a coloured precipitate
The higher the concentration of reducing sugar, the further the colour change goes. Blue > green > yellow > orange > brick red
Starch = iodine
Add iodine to the test sample
If starch is present, the sample will change from browny-orange to blue-black
If there is no starch, it stays browny-orange
Lipids - Emulsion test
Shake the test substance with ethanol for about a minute until it dissolves, then pour the solution into water
If there are any lipids present, they will precipitate out of the liquid and show up as a milky emulsion
The more lipid there is, the more noticeable the milky colour will be
Proteins - Biuret test
Add a few drops of potassium hydroxide solution to make it alkaline
Add some copper(II) sulfate solution
If there is no protein, the solution will stay blue
If protein is present, the solution will turn purple
Calorimetry
Weigh a small amount of food and skewer it on a mounted needle
Add a set amount of water to a boiling tube held with a clamp
Measure the temperature of the water, then set fire to the food using a Bunsen burner flame. Make sure the Bunsen burner isn't near the water
Immediately hold the burning food under the boiling tube until it goes out. Relight the food and hold it under the tube again - keep doing this until the food won't catch fire again
Measure the temperature of the water again
Energy in food (joules) = Mass of water (grams) x temperature change of water (degreesC) x 4.2
Energy per gram of food (joules per gram) = energy in food (joules) / mass of food (grams)
SB1g - Enzyme action
The active site is where the substrate of the enzyme fits at the start of the reaction
Different enzymes have different shaped active sites, so each enzyme can only work with specific substrates that fit the active site
Changes in pH or temperature can affect how the protein folds up, and so can affect the shape of the active site
If the shape of the active site changes too much, the substrate will not fit properly, so the enzyme will no longer catalyse the reaction. We call this denatured
SB1h - Enzyme activity
Temperature
When the temperature gets too high, the shape of the enzyme molecule starts to change. The amount of change increases as the temperature increases. So it becomes more and more difficult for a substrate molecule to fit into the active site
The temperature at which the enzyme works fastest is called the optimum temperature
As the temperature increases, molecules move faster, and higher speeds increase the chance of substrate molecules bumping into enzyme molecules and slotting into the active site
pH
If the pH is too high or low, the pH interferes with the bonds holding the enzyme together, changing the shape of the active site and denaturing the enzyme
All enzymes have an optimum pH that they work best at
Substrate concentration
The higher the substrate concentration, the faster the reaction, because it is more likely that the enzyme will meet up and react with a substrate molecule
However, after a point there are so many substrate that all the active sites are full, and adding more will make no difference
SB1i - Transporting substances
Diffusion
The gradual movement of particles from places of high concentration to places of lower concentrations
Diffusion happens in liquids and gases because particles in these substances are free to move about randomly
Only very small molecules can diffuse through cell membranes - things like glucose, amino acids, water and oxygen. Big molecules like starch and proteins can't fit through the membrane
Osmosis
The movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration
A partially permeable membrane has very small holes in it, only tiny molecules (such as water) can fit through
The water molecules will move from one side to another to dilute the more concentrated solute solution
Active transport
The movement of particles across a membrane against a concentration gradient using energy transferred during respiration
Particles move up a concentration gradient and the process requires energy from the mitochondria, which gives energy to the protein carriers