Eukaryotic and Prokaryotic Cell

Eukaryotic and Prokaryotic Cell Functions

• All living things are made of prokaryotic or eukaryotic cells.
• Animal and plant cells are eukaryotic.
• Eukaryotic cells have a cell membrane, cytoplasm, and a nucleus containing DNA.
• Bacterial cells are prokaryotic and much smaller than eukaryotic cells.
• Prokaryotic cells possess a cell wall, cell membrane, cytoplasm, a single circular strand of DNA, and plasmids.
• Organelles are structures within a cell with different functions.
• Organelles perform specific functions.

Animal and Plant Cell Structures and Functions

• The nucleus contains DNA coding for protein synthesis and is enclosed in a nuclear membrane.
• Cytoplasm facilitates chemical reactions and contains enzymes and organelles.
• The cell membrane controls the entry and exit of substances.
• Mitochondria facilitate aerobic respiration, providing energy.
• Ribosomes are where protein synthesis occurs.
• Chloroplasts facilitate photosynthesis by containing chlorophyll that harvests light to provide food for the plant.
• The permanent vacuole stores cell sap, is found within the cytoplasm, and supports cell rigidity.
• The cell wall is made of cellulose, provides strength, and is present in algal cells.

Bacterial Cell Structures and Functions

• The cytoplasm facilitates chemical reactions and contains enzymes and organelles.
• The cell membrane controls the entry and exit of substances.
• The cell wall is made of peptidoglycan.
• Chromosomal DNA floats in the cytoplasm, as bacterial cells have no nucleus.
• Plasmids are small rings of DNA that code for extra genes.
• Flagella are long, thin, whip-like tails that allow bacteria to move.

Specialised Cells and Their Functions

• Cells specialize through differentiation by gaining new subcellular structures to suit their roles.
• Cells can differentiate early or throughout their lives (stem cells).
• Animal cells mostly differentiate once, but plant cells can retain this ability.

Animal Specialised Cells

• Sperm cells are specialised to carry male DNA to the egg for reproduction.
• Sperm cells have streamlined heads and long tails which aid swimming.
• Sperm cells have many mitochondria, which supply energy for movement.
• The acrosome contains digestive enzymes to break down the outer layers of the egg cell membrane.
• Sperm cells have a haploid nucleus containing 23 chromosomes.
• Egg cells are specialised to receive sperm cells and develop into an embryo.
• The egg cell membrane is specialised to only allow one sperm cell inside during fertilisation.
• Egg cells have lots of mitochondria to provide energy for the developing embryo.
• Egg cells have large size and cytoplasm that allows quick cell division as the embryo grows.
• Ciliated epithelial cells waft bacteria trapped by mucus to the stomach.
• Cilia are hair like projections that waft bacteria to the stomach to be killed by stomach acid.

Plant Specialised Cells

• Root hair cells take up water by osmosis and minerals by active transport from the soil.
• Root hair cells have a large surface area due to root hairs, meaning there is more space for water to move in
• Root hair cells have a large permanent vacuole that affects the speed of movement of water from the soil to the cell
• Root hair cells have mitochondria to provide energy from respiration for the active transport of mineral ions.
• Xylem cells transport water and mineral ions from the roots to the shoots.
• During xylem cell formation, lignin is deposited and causes the cells to die, becoming a hollow tube for water and mineral ions to move through
• Lignin is deposited in spirals that helps xylem cells withstand pressure from watermovement.
• Phloem cells transport the products of photosynthesis to all parts of the plant.
• Sieve plates are cell wall structures that form and allow movement of substances from cell to cell.
• Mitochondria in companion cells supply energy because phloem cells lose many sub-cellular structures.

Microscopy

• Microscopes are needed to view extremely small cells.
• Robert Hooke observed the first cork cells in 1665 using a light microscope.
• Light microscopes have two lenses and are illuminated from underneath.
• Light microscopes have a maximum magnification of about 2000x and a resolving power of 200nm.
• Light microscopes can view tissues, cells, and large subcellular structures.
• Scientists developed electron microscopes in the 1930s to view deep inside sub-cellular structures.
• Electron microscopes use electrons instead of light, and electrons have a smaller wavelength than light waves.
• Scanning electron microscopes create 3D images, while transmission electron microscopes create 2D images that detail organelles.
• Electron microscopes have a magnification of up to 2,000,000x and resolving power of 10nm (SEM) and 0.2nm (TEM).
• Transmission electron microscopes have helped discover viruses.

Microscopy Calculations

• To calculate magnifications of a light microscope: magnification of the eyepiece lens x magnification of the objective lens
• To calculate the size of an object use: size of image/magnification = size of object
• Ensure measurements are in the same units when rearranging the equation.

Standard Form

• Standard form can be useful when working with large and small numbers.
• Multiplying a number by a power of 10 makes it bigger or smaller.
• A number being multiplied by a power of 10 should be between 1 and 10 to easily compare numbers.

Orders of Magnitude in Cells

• Orders of magnitude can be used to understand difference in sizes of cells, or organelles
• If an object is 10 times bigger than another, it can be said that it is 10 to the power of 1 times bigger
• In contrast, if something is smaller that will be presented as a negative power

Prefixes

• Prefixes go before units of measurement to show the multiple of the unit.
• Centi means multiply unit by 0.01.
• Milli means multiply unit by 0.001.
• Micro means multiply unit by 0.000, 001.
• Nano means multiply unit by 0.000, 000, 001.

Estimations

• Estimations help when exact counts are not possible or practical.
• Estimations work through sampling and multiplying.

Core practical: Investigating Biological Specimens

• To use a microscope, place the slide, focus the image, start with lowest objective lens magnification, and increase magnification while refocusing.

Preparing Slides

• Preparing a slide is a key step to a microscopy experiment.
• Thin layers of cells are peeled off or taken using a cotton bud, a chemical stain is applied to enhance visibility, the cells are applied to a glass slide, and a coverslip is carefully lowered to avoid air bubbles.

Microscopy Calculations

• Magnification = measured size / actual size
• Actual size = measured size / magnification
• Total magnification = objective lens magnification x eyepiece lens magnification

Enzymes - Catalysts

• Enzymes are biological catalysts that increase reaction rates without being used up.
• Enzymes are proteins with a uniquely shaped active site where substrates bind.
• Enzymes catalyse many reactions meaning cells can control what binds to them.
• Enzymes form what is called an enzyme-substrate complex.
• Enzyme specificity is when enzymes can only catalyse reactions, only when the complementary shaped substrate binds to the active site.

Optimising Enzymes

• Enzymes need an optimum pH and temperature to work.
• Excessive temperatures can break the bonds holding the enzyme together,
• Denaturing of the enzyme changes the active site, preventing substrate binding.
• Denaturing of the enzyme renders them unable to work.
• The best pH for most enzymes is pH 7 (neutral).
• Extreme pH can affect the forces holding amino acids in the protein, changing the active site shape preventing the substrate from binding.

Substrate Concentration

• Substrate concentration affects enzyme action by increasing the rate of reaction up to a point called the saturation point.
• The rate at which enzyme-substrate complexes form increases as the substrate concentration increases.

Core Practical - Effect of pH on Enzyme Activity

• Amylase breaks down carbohydrates like starch into simple sugars like maltose.
• Iodine (dark orange) shows if starch if present by turning blue-black.
• We can use this knowledge to estimate amylase optimal pH

Enzymes - Materials Required

• The materials required are: 1% amylase solution, 1% starch solution, iodine solution, and labelled buffer solutions of different pH
• First place single drops of iodine solution on each well of a tray.
• Then label a test tube with the pH to be tested, and place it in a water beaker with 50ml cold water and place this above a Bunsen Burner for 3 minutes.
• Next place 2cm³ of amylase solution, 2cm³ of starch solution and 1cm³ of the buffer pH solution in a test tube and start a stopwatch.
• After 10 seconds, use a pipette to place a drop the solution into one of the wells containing iodine solution.
• Repeat Step 4 after another 10 seconds, continuing until the solution remains orange, and record the time taken
• Continue repeating the method with a different pH each time.
• Finally results are shown on a graph of pH (on the x-axis) and time taken to complete reaction (on the y-axis).

Enzyme Activity Controls

• We use a Bunsen Burner and water beaker in order to keep the temperature the same, as temperature needs to be a control variable in this experiment
• The optimal pH of amylase will be at whichever pH the reaction completes in the shortest amount of time. This is likely to be pH 7

Rate Calculations

• Rate calculations can be performed using the formula: Rate = Change / Time
• Change refers to the measurement that is being carried out, in this case an enzyme measurement

Enzyme Examples

• Carbohydrases convert carbohydrates into simple sugars.
• Amylase, a type of carbohydrase, breaks down starch into maltose is produced in the salivary glands, pancreas and small intestine.
• Proteases convert proteins into amino acids.
• Pepsin, a type of protease, breaks down proteins into amino acids and is produced in the stomach, small intestine and pancreas.
• Lipases convert lipids (fats) into fatty acids and glycerol.
• Lipase is produced in the pancreas and small intestine.

Soluble Products

• Soluble glucose, amino acids, fatty acids, and glycerol pass into the bloodstream to supply cells, which are used to build complex molecules

Food Tests

• Food tests identify starch, reducing sugars, proteins, and lipids.

Starch Test

• Iodine solution is the test to identify starch in a food sample.
• If a food sample is positive for starch, iodine turns from orange to blue-black.

Reducing Sugars Test

• Benedict's solution is the test to identify reducing sugars in a food sample.
• For this experiment, mix 2cm3 Benedict's solution and 2cm3 of test solution and heat in hot water bath for 5 mins.
• A postive test will show a colour change to browny-red.

Protein Test

• The Biuret test with potassium hydroxide and copper sulfate helps identify proteins in food samples.
• Mix potassium hydroxide and copper sulfate with a food sample, a positive test will show a colour change toviolet.

Lipid Test

• The emulsion test is used to test food samples for lipids.
• Mix ethanol with food, then mix this with deionised water, a positive test will produce a white emulsion layer.

Calorimetry

• Calorimetry measures the energy in food.
• Adding a burning food sample to a test tube with cold water will cause the final temperature to increase in the water.
• Energy transferred = mass of water x 4.2 x temperature increase
• Energy transferred is measured in Joules (J).
• The mass of water is measured in grams (g).
• Temperature increase is measured in degrees Celsius.

Transport across Cell Membrane

• Oxygen, glucose, and waste products transport across the cell membrane which are key to life processes.
• Diffusion is when molecules move from a high concentration to a low concentration.
• Osmosis applies only to water, moving from a dilute solution to a more concentrated solution across a selectively permeable membrane.
• Active transport requires energy (ATP) to move molecules against a concentration gradient.

Core Practical - Osmosis in Potatoes

• Change in mass of potato disks in sucrose solutions can be observed to measure osmosis.
• Cut potato disks of equal size, blot excess water, measure initial mass, place in sucrose solutions (1%, 2%, etc.), blot again, and record new mass.
• Find the difference in mass (end mass - start mass) and use the percentage change equation to find the percentage gain or loss of mass.
• We are changing the concentration of the sucrose solution, the independent variable.
• We are measuring the change in mass of the potato disks, the dependent variable
• We are controlling the diameter of the disks (2cm), the control variable.
• Water moves by osmosis from a dilute solution (in potato) to a concentrated solution (sucrose solution) through a selectively permeable membrane.