Cell Structure and Function

Cells Overview

• All life is composed of cells.
• Light microscopes can visualize cells, possibly with the nucleus visible.
• Electron microscopes can visualize subcellular structures in fine detail with higher resolving power and resolution.
• Magnification = Image size / Object size can be rearranged to calculate actual cell size (Actual cell size = Image size / Magnification).
• Eukaryotic cells contain a nucleus where DNA is stored (e.g., plant and animal cells).
• Prokaryotic cells lack a nucleus; their DNA is in a ring called a plasmid.
• Cell membranes are semi-permeable, allowing certain substances to pass through.
• Plant cells and most bacteria have a cell wall (cellulose in plants) for rigid structure.
• Cytoplasm is the liquid within cells where chemical reactions occur.
• Mitochondria are the sites of respiration, releasing energy.
• Ribosomes are where proteins are assembled/synthesized.
• Plant cells contain chloroplasts with chlorophyll for photosynthesis.
• Plant cells contain a permanent vacuole for sap storage.

Bacteria

• Bacteria multiply via binary fission.
• Aseptic technique: sterilizing equipment and using a flame to prevent contamination.
• Bacteria culture in a Petri dish: tape the dish to allow air to enter for aerobic respiration during incubation, incubate at 25°C.
• Calculate the size of the culture from an initial drop or the area in which bacteria did not grow or were killed by an antibiotic to then compare with others
• Use πr² or πd²/4 to calculate the area of the circles.

Chromosomes and Mitosis

• Eukaryotic cell nuclei contain DNA stored in chromosomes; humans have 23 pairs (diploid).
• Gametes have half the number of chromosomes (23, haploid).
• Mitosis is the process where new cells are made for growth and repair.
• Genetic material is duplicated during mitosis.
• The nucleus breaks down, and chromosome sets are pulled to opposite sides of the dividing cell.
• Two identical cells are formed; AQA states the nucleus divides.

Cell Specialization & Stem Cells

• Cells specialize based on their function (e.g., nerve, muscle, root hair, xylem, phloem).
• Stem cells are unspecialized cells found in embryos and the meristem of plants.
• Bone marrow stem cells can only specialize into blood cells.
• Stem cells can potentially combat conditions like diabetes and paralysis.
• Cloning plants can prevent extinction or produce crops with specific traits.

Diffusion, Osmosis & Active Transport

• Diffusion is the movement of molecules from high to low concentration (down the concentration gradient).
• Diffusion is a passive process, requiring no energy input.
• Osmosis: diffusion of water across a semi-permeable membrane.
• Rate of diffusion/osmosis: increase with a greater concentration difference, temperature, or surface area.
• Osmosis practical: cut equal size cylinders from a potato, measure the mass of each, and put into varying sugar solutions. remove after a day, dry the excess water and remeasure and calculate % change to compare results.
• Plot these percentages against sugar concentration and draw a line of s fit where this crosses the x-axis is what concentration should result in no change in mass so no osmosis.
• Active transport: carrier proteins use energy to move substances across a membrane against the concentration gradient (e.g., mineral ions into root hair cells).

Tissues, Organs, and Organ Systems

• Similar cells connected form tissues (e.g., heart tissue).
• Tissues form organs (e.g., the heart).
• Organs work together in organ systems (e.g., the circulatory system).
• The digestive system breaks down food into nutrients.
• Bile, made in the liver and stored in the gallbladder, neutralizes stomach acid and emulsifies fats.

Enzymes

• Enzymes are biological catalysts.
• Enzymes break down larger molecules into smaller ones.
• Amylase breaks down starch into glucose.
• Carbohydrases break down carbohydrates into simple sugars.
• Proteases break down proteins into amino acids.
• Lipases break down lipids (fats) into glycerol and fatty acids.
• The rate of enzyme activity increases with temperature until the enzyme denatures.
• Optimum temperature is where maximum rate occurs.
• Optimum pH is where maximum rate occurs also; too high or low pH can denature enzymes.
• Practical on enzyme activity: mix amylase with starch at different temperatures or pH, check for starch breakdown with iodine.

Food Tests

• Iodine turns blue/black in the presence of starch.
• Benedict's solution turns blue to orange in the presence of sugars.
• Biuret reagent turns blue to purple with proteins.
• Cold ethanol goes cloudy with lipids (fats).

Respiratory System

• Air moves down the trachea to bronchi, then to bronchioles, and finally to alveoli.
• Alveoli: air sacs where gas exchange occurs.
• Oxygen binds to hemoglobin in red blood cells.
• Carbon dioxide is dissolved in the plasma of the blood.

Circulatory System

• The heart is at the center; blood enters the heart twice in each cycle (double circulatory system).
• Deoxygenated blood enters the right atrium via the vena cava.
• Blood moves through the pulmonary artery to the lungs for oxygenation.
• Oxygenated blood returns to the left atrium via the pulmonary vein.
• Blood pumps through the aorta to the body from the left ventricle.
• Arteries carry blood away from the heart (oxygenated, except for the pulmonary artery).
• Veins carry blood toward the heart (deoxygenated, except for the pulmonary vein).
• Arteries have thicker walls and a narrower lumen.
• Veins have thinner walls and valves to prevent backflow.
• Capillaries: tiny vessels with one-cell-thick walls for fast diffusion.
• Coronary artery supplies the heart muscle with blood.
• Blockage leads to CHD (coronary heart disease) and heart attack.
• Stents keep blood vessels open.
• Statins reduce cholesterol and fatty deposits.
• Faulty heart valves can be replaced with artificial ones.
• Blood contains plasma, red blood cells, white blood cells, and platelets.
• Platelets clump to clot wounds and stop bleeding.

Diseases

• CVD (cardiovascular disease) is a non-communicable disease.
• Obesity and too much sugar can cause type 2 diabetes.
• Bad diet, smoking, and lack of exercise increase the risk of heart disease.
• Alcohol can cause liver diseases.
• Smoking can cause lung disease or cancer.
• Carcinogens increase the risk of cancer.
• Cancer is caused by damaged cells dividing uncontrollably.
• Benign cancers don't spread; malignant cancers do.

Plant Structure and Transpiration

• Leaves: photosynthesis and transpiration.
• Roots: water and mineral ion entry.
• Meristem: new cells are made.
• Xylem: unidirectional water transport.
• Phloem: bidirectional sugar (food) transport (translocation).
• Rate of transpiration: increases with higher temperature, decreased humidity, and increased air movement.

Plant Deficiencies

• Nitrate deficiency stunts growth (needed for protein synthesis).
• Chlorosis (yellowing of leaves) can be due to magnesium deficiency.
• Magnesium is needed to make chlorophyll.

Leaf Structure

• Waxy cuticle: waterproof layer to prevent water evaporation.
• Upper epidermis: transparent cells allowing light penetration.
• Palisade mesophyll: the main site of photosynthesis with many chloroplasts.
• Spongy mesophyll: airspace for gas exchange.
• Vascular bundle: contains xylem and phloem.
• Lower epidermis: contains stomata for gas exchange.
• Stomata are controlled by guard cells.

Infection and Response

• Communicable diseases: caused by pathogens (viruses, bacteria, fungi, protists).
• Viruses: genetic code in a protein casing that injects into cells to replicate itself.
• Measles: a virus spread by droplets, causing a rash.
• HIV: an STD which compromises the immune system (AIDS).
• Bacteria: release toxins that damage body cells (e.g., salmonella, gonorrhea).
• Fungi: can cause infections like athlete's foot.
• Protists: single-celled parasites (e.g., malaria spread by mosquitoes).
• Rose black spot: a fungal infection in plants.
• Tobacco mosaic virus: inhibits chlorophyll production, causing stunted growth.
• Body defenses: skin, mucus, stomach acid, enzymes.
• White blood cells: lymphocytes and phagocytes.
• Lymphocytes: produce antitoxins and antibodies.
• Antibodies: stick to antigens on pathogens, preventing infection.
• Phagocytes ingest and destroy pathogens.
• Immunity: immune system stores a copy of the antibody and antigen.
• Vaccines: dead or inert pathogens that expose the immune system, stimulating antibody production.
• The Flu vaccine consists of a irradiated virus injected into the body, so it cannot perform its function, or harm the patient.
• The Covid mRNA vaccine consists synthetic DNA that is injected into the body, to teach your cells to create antigens so that the body can fight of any infection.
• Antibiotics: kill bacteria but not viruses; penicillin was the first.
• Bacteria mutate, becoming resistant to antibiotics.
• Drugs: extracted from plants/organisms or synthesized.
• Drug trials: lab trials on cells/tissue, animal trials, human trials (with placebo control groups).
• Blind trial: test subjects don't know if they're taking the drug or placebo.
• Double-blind trial: even analysts don't know which group is which.
• The Flu vaccine consists of a irradiated virus injected into the body, so it cannot perform its function, or harm the patient.
• The Covid mRNA vaccine consists synthetic DNA that is injected into the body, to teach your cells to create antigens so that the body can fight of any infection.

Monoclonal Antibodies

• Created from clones of cells that can produce specific antibodies.
• Hybridoma cell: lymphocytes are combined with tumor cells.
• The Downside to monoclonal antibodies are that the side effects from them are worse than scientists expected.
• Used for medical diagnosis, pathogen detection in labs, and identifying molecules in tissue through dyes.

Photosynthesis

• Photosynthesis occurs in chloroplasts in plant cells.
• Word equation: Carbon dioxide + Water → Glucose + Oxygen
• Balanced chemical equation: 6CO2 + 6H2O → C6H12O6 + 6O2.
• Photosynthesis requires energy (endothermic reaction).
• Glucose is used for respiration, stored as starch/fat, or used to produce cellulose and amino acids.
• The rate of photosynthesis increases with higher temperature (unless enzymes denature), higher light intensity, and higher CO2 concentration.
• Limiting factor: the factor in shortest supply that limits the rate of photosynthesis.
• Light intensity follows an inverse square relationship.
• The Practical on measuring photosynthesis involved using pondweed to measuring the volume of oxygen production and the rate of photosynthesis.

Respiration

• Eukaryotic Cells respire in the mitochondria
• Word equation: chemical code and structure for the reactions
• Aerobic respiration: Glucose + Oxygen → Carbon dioxide + Water
• Balanced chemical equation: C6H12O6 + 6O2 → 6CO2 + 6H2O.
• Breathing and heart rates increase during exercise.
• Anaerobic respiration: Glucose → Lactic acid (less energy released).
• Oxygen debt occurs afterward to break down lactic acid in the liver back into glucose.
• Anaerobic respiration in plants/yeast: Glucose → Ethanol + Carbon dioxide.
• The practical on how yeast cells respire turns glucose into ethanol and carbon dioxide
• Fermentation is used to make alcoholic drinks and bread.

Metabolism

• Metabolism: sum of all reactions in a cell or organism.
• Includes respiration, conversion of glucose into starch/glycogen/cellulose.
• Glucose + Nitrates → Amino acids for protein synthesis.
• Fatty acids + Glycerol → Lipids.
• Breakdown of excess proteins → Urea.