General overview (key concepts in Biology)

Sub-cellular structures of animal cells

Mitochondria, nucleus, cell membrane, ribosomes

Sub-cellular structures in plant cells

Nucleus, mitochondria, cell membrane, ribosomes, chloroplasts, cell wall, large permanent vacuole

Sub-cellular structures in bacteria cells

Chromosomal DNA, plasmid DNA, cell membrane, ribosomes, flagellum

What is the function of the nucleus?

Contains genetic information and controls cell activities

What is the function of the cell membrane?

Controls what enters and exits the cell

What is the function of the mitochondria?

Carry out aerobic respiration

What is the function of the ribosomes?

Protein synthesis

What is the function of the cell wall?

Provides support and strengthens the plant cell

What is the function of chloroplasts?

Contain chlorophyll and is where photosynthesis occurs

What is the function of the large, permanent vacuole?

Keeps the cell swollen and rigid (turgid)

What is the function of chromosomal DNA?

Contains the genetic information of the bacteria cell

What is the function of plasmid DNA?

Gives variation between bacterium and can move from one bacterium to another

What is the function of the flagellum?

Allows the bacterium to move through liquids

How are sperm cells adapted to their function?

Acrosome: contains digestive enzymes so the sperm can penetrate the egg

Haploid nucleus: contains the genetic material for fertilisation

Mitochondria: provide energy for sperm to swim

Flagella: allows the sperm to swim

How are egg cells adapted to their function?

Cytoplasm: contains nutrients for developing the egg

Haploid nucleus: contains genetic material for fertilisation

Cell membrane: changes after fertilisation by a single sperm so no more can enter

How are ciliated epithelial cells adapted to their function?

Cilia: waft to move fluids and particles

What are the two types of cells?

Eukaryotic and prokaryotic

What is the difference between eukaryotic and prokaryotic cells?

Eukaryotic cells contain membrane bound organelles while prokaryotic cells do not

What are the advantages of light microscopes?

Inexpensive, easy to use, portable, can observe both living and dead specimens

What is the disadvantage of light microscopes?

Limited resolution

What are the advantages of electron microscopes?

Greater magnification and resolution

What are the disadvantages of electron microscopes?

Expensive, less portable, require training to use, only dead specimens can be observed

Parts of a light microscope

Eyepiece lens, stage, objective lens, fine focusing knob, rough focusing knob

How do you use a light microscope?

Place the slide onto the stage and look through the eyepiece lens. Start with the lowest powered objective lens. Turn the focusing knobs to obtain a clear image. Choose a higher powered objective lens and refocus

How do you prepare a slide?

Take a thin layer of cells from your sample using tweezers or a cotton bud (for an onion or cheek cell sample etc). Place the layer of cells onto the glass slide. Add a few drops of stain to make smaller structures more visible on the microscope. Lower a coverslip carefully onto the slide, avoiding air bubbles

Magnification formula

Magnification=image size/actual size

What is an enzyme?

A biological catalyst that doesn’t get used up or chemically changed in a reaction

Describe the lock and key hypothesis

The substrate binds to the active site of an enzyme if its shape is complimentary to the active site, to form an enzyme-substrate complex. The substrate is converted into products, which are released from the enzyme

How is the lock and key model flawed?

Recent research has proven that enzymes change the shape of their active site slightly to bind better to the substrate - the lock and key model suggests that the enzyme’s active site is a fixed shape

How does temperature increase affect enzyme activity?

As temperature increases, molecules gain kinetic energy. The more movement of the molecule creates more successful collisions so more enzyme-substrate complexes form, leading to a higher rate of reaction. If temperature goes above the optimum (37.5 degrees C), the enzyme bonds are broken and the active site becomes denatured. No substrate can fit into the denatured site so there are no enzyme-substrate complexes so the rate of reaction decreases

How does pH affect enzyme activity?

Enzymes have an optimum pH with a high rate of reaction. If pH changes, the active site changes through denaturing, decreasing the rate of reaction

How does substrate concentration affect enzyme activity?

As substrate concentration increases, number of molecules in the same volume increases, so the probability of successful collisions increases. More enzyme-substrate complexes form, and the rate of reaction increases. Once all of the active sites are full, the rate of reaction plateaus

Investigating how pH affects enzyme activity core practical

Place a drop of iodine solution into wells of a dimple tray. Label a test tube with the pH to be tested, placing it into a water beaker with 50ml cold water. Heat this using a Bunsen burner for three minutes. Place 2cm³ of starch solution and 1cm³ of the pH solution in the test tube and start a stop watch. After every 10 seconds, place a drop of the solution into a well of the dimple tray and monitor the colour change, noting the time it takes for the iodine to turn blue or black, indicating the presence of starch. Repeat with different pHs and record the results.

Formula for rate

Rate=1/time

What enzyme breaks down starch and what is the test?

Amylase breaks starch into simple sugars

Test for starch: iodine solution turns from orange/yellow to blue/black if present

What enzyme breaks down reducing sugars (including glucose) and what is the test?

Carbohydrase breaks reducing sugars into simple sugars

Test for reducing sugars: Benedict’s solution placed into a hot water bath for 5 minutes will turn it from blue to red if present

What enzyme breaks down protein and what is the test?

Protease breaks down protein into amino acids

Test for protein: add Biuret’s solution to a test tube with the substance to be tested and shake/mix well. It will turn from blue to lilac if present

What enzyme breaks down lipids and what is the test?

Lipase breaks down lipids into fatty acids and glycerol

Test for lipids: add ethanol and water to the sample and shake well. A white emulsion will form if present

Describe the process of calorimetry

Record the starting temperature of 50ml of water, place a test tube with the water at a 45 degree angle and hold a sample of burning food underneath it. When the food has finished burning, record the final temperature of the water

What is the formula for energy transfer in calorimetry?

Energy transferred=mass of waterx4.2xchange in temperature

What is diffusion?

The net movement of particles from an area of high concentration to an area of low concentration. It is a passive process

What is osmosis?

The net movement of water molecules from a dilute solution (high concentration of water) to a concentrated solution (low concentration of water) through a partially permeable membrane. It is a passive process

What is active transport?

The movement of molecules against the concentration gradient, from a low concentration to a high concentration. It requires energy (is an active process)

Osmosis in potatoes core practical

Cut potatoes into cubes of equal size and dry to remove excess water. Measure the initial mass of each cube. Place the cubes in sucrose (a type of sugar) solutions of different concentrations in a time frame (such as 2 minutes). Remove and dry the potatoes, recording the new mass. Subtract the new mass from the original mass to record the change in mass