Topic 1 - Key Concepts In Biology Flashcards
1.1 - How are sub-cellular structures of eukaryotic cells related to their function?
A cell with a nucleus is a eukaryotic cell.
Animal cells are eukaryotic and have a:
Nucleus - controls the cell and its activities, contains DNA.
Cell membrane - Controls what enters and leaves the cell.
Mitochondria - Where aerobic respiration happens.
Cytoplasm - A jelly-like substance where chemical reaction occur.
Ribosomes - Found in the cytoplasm, where they make new proteins.
Another eukaryotic cell is a plant cell, they contain everything an animal cell has but also has:
Cell wall - made of cellulose and maintains rigidity of the cell.
Chloroplasts - contain chlorophyll which traps energy transferred from the Sun for photosynthesis.
Vacuole - contains cell sap to help the rigidity of the cell.
1.1 - How are sub-cellular structures of prokaryotic cells related to their function?
A cell without a nucleus, mitochondria and chloroplasts is a prokaryotic cell.
Bacterial cells are prokaryotic and have a:
Chromosomal DNA - controls most cell activities.
Plasmid DNA - controls come cell activities.
Cell membrane - Controls what enters and leaves the cell.
Ribosomes - Found in the cytoplasm, where they make new proteins.
Flagella - Spins for the bacterium to move.
1.2 - How are reproductive cells specialised for reproduction?
Sperm cells - lots of mitochondria in the middle of the body, to release energy for the tail.
Head contains a vacuole called the acrosome, which has enzymes that break down the egg cell’s outer layer.
Has streamlined shape and tail moves side to side to swim.
Egg cells - after fusing with a sperm, the membrane becomes hard, to stop more sperm cells entering the egg.
Its cytoplasm is packed with nutrients, to supply the fertilised egg cell for growth of the embryo.
Ciliated epithelial cells - Fertilisation happens in the oviduct of a female.
Cells in oviduct lining transport egg cells to the uterus.
These cells are adapted by having hair-like cilia, which wave from side to side to move substances.
Cells lining the body are epthelial cells, if they have cilia, they are ciliated epithelial cells.
1.2 - What happens during reproduction?
Two specialised cell/gametes fuse to create a cell that becomes an embryo.
Human gametes are the egg and sperm cell.
Human nuclei usually contain two copies of 23 chromosomes, these are diploid cells.
Gametes only have one copy of 23 chromosomes, these are haploid cells.
1.3 - How has the development of microscopes allowed better research?
The light microscope developed by Hooke had a magnification of 30x.
The resolution is the smallest distance between two points.
Nowadays, there are better lenses and light for microscopes, this makes the light microscope magnify up to 1500x and a resolution of 0.0001mm.
Although the electron microscope uses beams of electrons through a specimen, it can magnify up to 2,000,000 and a resolution of 0.0000002mm or 2 * 10^7.
This microscope allows more detail and clarity.
1.4 - How can we find out the magnification of a microscope and estimate cell sizes?
Magnification = Eyepiece * Objective lens
The circular area seen in a microscope is the field of view,
If we know the diameter of the field of view, you can find the length of cells using ratios.
Scale Bars are shown on micrographs to estimate sizes.
1.5 - What units are used for small sizes?
milli - 10^-3
micro - 10^-6
nano - 10^-9
pico - 10^-12
divide by 1000 every time.
1.6 - Core Practical: Investigate biological specimens using microscopes
Peel the epidermis of an onion cell using tweezers.
Add an iodine stain to the centre of a microscope slide.
Place the specimen on the stain and use a toothpick to lower a coverslip on the specimen. This keeps the specimen flat and in place.
Examine the specimen from lowest to highest magnification.
Draw the cells seen and annotate the structures of it.
1.7 - Explain how an enzyme works
Enzymes are 3D proteins formed by amino acids, this 3D shape is caused by the folding of the chain.
This 3D shape is important as in it, there is a pocket called the active site.
The active site is where the substrate of the enzyme fits at the start of a reaction.
Different substrates have different shapes and different enzymes have different active site shapes.
Therefore enzymes only work with specific substrates that fit the active site.
1.7 - What is the lock and key model?
A model of how an enzyme and substrate fit together.
The active sire holds the molecules in position for bonds to form and make a product.
Product molecules are slightly different shapes so it no longer fits tightly in the active site and is released.
1.8 - How can enzymes be denatured?
Changes in pH or temperature can affect how a protein folds and its shape.
If the shape of the enzyme changes too much, the substrate won’t fit.
If the active site changes shape too much, the enzyme won’t catalyse the reaction.
These changes denature the enzyme.
1.9 - How is enzyme activity affected by temperature, substrate concentration and pH?
pH - Rate of reaction is highest at the optimum pH, at pH’s below and above the optimum, the active site’s shape is affected and the enzyme isn’t as active.
Substrate concentration - At high concentrations, most enzyme active sites have enough of the substrate and the rate of reaction is fast as it can be.
At low concentrations, many enzyme molecules have empty active sites so rate of reaction is slow.
Temperature - As it increases, molecules move faster. Higher speeds increase chance of substrate molecules colliding into enzyme molecules where they react.
When temperature is too high, the shape of the enzyme molecule changes making it harder for a substrate to fit in the active site.
The temperature where the enzyme works the fastest is the active site.
1.10 - Core Practical : Investigate the effect of pH on enzyme activity
Set up a heating apparatus with a tripod, gauze, heat resistant mat, Bunsen burner and large beaker half-filled with water.
Heat water to 40°C and keep the temperature constant.
Place a drop of iodine solution into each depression of a well tray.
Measure 2cm^3 of amylase solution into a tube.
Add 1cm^3 of a solution with a noted pH into the tube.
Add 2cm^3 of starch solution to the tube and place in water bath. Start timer and stir.
Add a drop of the solution to the tray every 20 seconds. Stop when iodine changes colour.
Blue/Black colour indicated the presence of starch, so the amylase didn’t work.
Yellow/Orange colour indicates the reaction is complete, so the amylase worked.
Repeat the experiment using different pH’s.
1.11 - How do you calculate the rate of enzyme activity on a graph?
If 100g of starch is broken down in five mins, reading off a graph:
100/5 = 20g/min is the rate of reaction.
1.12 - How are foods broken down into monomers?
Digestive enzymes turn large molecules into smaller molecules, these smaller molecules are absorbed into the small intestine.
Proteins are broken down into amino acids.
Starch molecules are broken down into glucose molecules.
Lipid molecules are broken into fatty acids and glycerol.