Cell Structure and Function

Cells

• Cells are the fundamental units of life.
• Light microscopes can reveal cells and their nuclei
• Electron microscopes provide higher resolving power and resolution, allowing visualization of subcellular structures (organelles).
• Magnification = Image size / Object size can be rearranged to calculate actual cell size.

Eukaryotic vs. Prokaryotic Cells

• Eukaryotic cells (plant and animal) contain a nucleus that houses DNA.
• Prokaryotic cells (bacteria) lack a nucleus.
• Both cell types share similar organelles and subcellular structures.
• The cell membrane encloses the cell and is semi-permeable, controlling substance passage.
• Plant cells and bacteria possess a cell wall (cellulose in plants), providing structural support.

Cell Components

• Cytoplasm: The liquid medium where chemical reactions occur.
• Mitochondria: Sites of respiration, releasing energy for the cell.
• Ribosomes: Locations of protein synthesis.
• Chloroplasts (plant cells): Contain chlorophyll for photosynthesis.
• Vacuole (plant cells): Stores cell sap.

Bacterial Reproduction

• Bacteria reproduce through binary fission (triple science only).
• Aseptic techniques prevent contamination in bacterial cultures including:
  • Flaming the dish opening to create air convection currents which carry microbes away
  • Sterilizing equipment
• Antibiotics can be tested on bacterial cultures by observing zones of inhibition (areas where bacterial growth is prevented).
• Petri dishes should be taped securely but with small opening to allow air in for aerobic respiration.
• Area calculations (πr², πd²/4) analyze culture size or antibiotic effectiveness.

Cell Nucleus and Division

• Eukaryotic nuclei contain DNA organized into multiple chromosomes.
• Human cells possess 23 pairs of chromosomes (diploid).
• Gametes (sex cells) contain 23 single chromosomes (haploid).
• Mitosis is the cell division process for growth and repair
• During mitosis:
  • Genetic material duplicates.
  • The nucleus breaks down.
  • Chromosomes move to opposite sides of the cell.
  • New nuclei form, resulting in two identical cells.

Cell Specialization and Stem Cells

• Cell specialization occurs to fulfill specific functions (e.g., nerve, muscle, xylem, phloem cells).
• Stem cells are undifferentiated cells found in embryos and plant meristems.
• Bone marrow stem cells produce blood cells.
• Stem cells offer potential for treating conditions like diabetes and paralysis.
• Cloning can create stem cell sources that are immunologically matched to patients, raising ethical concerns.
• Plant cloning aids species preservation and crop production.

Diffusion

• Diffusion is the passive movement of molecules from high to low concentration.
• It occurs across semi-permeable membranes if molecule size permits.

Osmosis

• Osmosis is specifically the diffusion of water across a semi-permeable membrane.
• Water moves to equalize solute concentrations, potentially affecting cell mass.
• Factors increasing diffusion/osmosis rate:
  • Increased concentration gradient
  • Increased temperature
  • Increased surface area

Osmosis Experiment

• To conduct an osmosis experiment:
  • Cut equal-sized potato cylinders.
  • Weigh cylinders and place in varying sugar solutions.
  • After a set time, reweigh and calculate percentage mass change.
  • Plot data to determine sugar concentration with no mass change (isotonic point).

Active Transport

• Active transport uses energy and carrier proteins to move substances against a concentration gradient.
• Example: Mineral ion uptake in plant root hair cells.

Levels of Organization

• Tissues: Groups of similar cells (e.g. heart tissue).
• Organs: Structures composed of different tissues (e.g., the heart).
• Organ systems: Groups of organs working together (e.g., the circulatory system).

Digestive System

• The digestive system breaks down food into absorbable nutrients.
• Stomach acid initiates breakdown
• Bile, produced in the liver and stored in the gallbladder, emulsifies fats. Also neutralizes stomach acid
• Enzymes are biological catalysts that break down molecules
  • Amylase: Breaks down starch into glucose
  • Proteases: Break down proteins into amino acids
  • Lipases: Break down lipids into glycerol and fatty acids
• Enzymes exhibit specificity based on the lock and key principle

Enzymes Rate of Reaction

• Enzyme activity rises with temperature until denaturation occurs at the optimum temperature.
• Extremes of pH can also cause denaturation.

Enzymes Experiment

• The rate of reaction of enzymes can be measured by:
  • Mixing amylase and starch at different temperatures or pH levels.
  • Timing how long it takes for starch to be broken down when iodine no longer turns black.
  • Plotting results to determine optimum conditions.

Food Tests

• Iodine: Indicates starch presence (orange to black).
• Benedict's solution: Indicates sugars presence (blue to orange).
• Biuret reagent: Indicates proteins presence (blue to purple).
• Ethanol emulsion test: Indicates lipids presence (cloudy).

Respiratory System

• Air travels from the trachea to the bronchi, then bronchioles, and finally to the alveoli.
• Alveoli: Air sacs with large surface area for gas exchange.
• Oxygen binds to hemoglobin in red blood cells for transport.
• Carbon dioxide is dissolved in blood plasma for removal.

Circulatory System

• The circulatory system is a double circulatory system with two circuits
• Deoxygenated blood enters right atrium via vena cava.
• Blood flows to right ventricle, then to pulmonary artery for oxygenation in lungs
• Oxygenated blood returns to left atrium via pulmonary vein.
• Blood flows to left ventricle, then to the aorta for distribution to the body.
• The heart's left ventricle has a thicker wall than the right ventricle.
• Electrical impulses in the heart cause muscle contraction.
• Artificial pacemakers regulate heart rhythm.

Blood Vessels

• Arteries carry blood away from the heart with thick walls and higher pressure.
• Veins bring blood back to the heart and have thinner walls and valves for backflow prevention.
• Capillaries: Tiny one-cell thick vessels that facilitate molecule exchange.

Heart Health

• The heart relies on the coronary artery for oxygen and blood supply.
• Blockage can lead to coronary heart disease (CHD) and potentially a heart attack.
• Stents: Open blocked arteries.
• Statins: Drugs that lower cholesterol.
• Artificial valves replace faulty heart valves.

Blood Components

• Plasma: Carries blood cells.
• Red blood cells: Transport oxygen.
• White blood cells: Fight infection.
• Platelets: Aid blood clotting.

Disease

• Communicable diseases are caused by pathogens that enter the body.
• Non-communicable diseases are caused by internal factors.
• Obesity/sugar can cause type 2 diabetes.
• Diet, smoking, and exercise can affect heart disease risk.
• Alcohol can cause liver disease.
• Smoking can cause lung disease/cancer.
• Carcinogens increase cancer risk.
• Cancer results from uncontrolled cell division and tumor formation.
• Benign tumors: Non-spreading and easily treated.
• Malignant tumors: Spreading and difficult to treat.

Plant Organs

• Leaves: Photosynthesis
• Roots: Water and mineral absorption.
• Xylem: Transports water unidirectionally.
• Phloem: Transports sugars bidirectionally (translocation).
• Meristem: New cell production.
• A higher temperature, lower humidity, and increased air movement all increase transpiration

Plant Deficiencies (Triple Only)

• Nitrate deficiency: stunts growth due to ineffective protein synthesis.
• Magnesium deficiency: causes chlorosis (yellowing of leaves) because magnesium is needed to make chlorophyll.

Leaf Structure (Triple Only)

• Waxy Cuticle: Waterproof layer that prevents water loss from the top of the leaf.
• Upper Epidermis: Transparent layer that allows light in.
• Palisade mesophyll: Layer with many chloroplasts for photosynthesis.
• Spongy mesophyll: Layer with air spaces for gas exchange.
• Vascular bundle: Contains xylem and phloem.
• Lower Epidermis: Bottom layer of leaf
• Stomata: Pores for gas exchange, controlled by guard cells.

Infection and Response

• Communicable diseases are caused by pathogens (viruses, bacteria, fungi, protists).
• Viruses inject genetic code into cells, forcing them to replicate the virus.

Infections

• Measles Virus: Spread by droplets.
• HIV: Sexually transmitted infection (STI) that attacks the immune system.
• Bacteria: Release toxins. Salmonella from undercooked food etc.
• Gonorrhea: Another STI.
• Fungi: Example is Athlete's foot
• Protists: Parasites which can affect any cell. Malaria for example.

Plant Diseases

• Rose black spot: Fungal infection treated with fungicides.
• Tobacco mosaic virus: Discolors leaves and stunts growth by inhibiting chlorophyll prodution.

Defenses

• Physical barriers: Skin
• Mucus in nose and trachea traps incoming pathogens.
• Stomach acid and digestive enzymes destroy pathogens.

White Blood Cells

• Lymphocytes:
  • Produce antitoxins to neutralize poisons.
  • produce antibodies specific to antigens on pathogens
• Phagocytes ingest and destroy pathogens.
• Clonal selection: Lymphocytes store antibodies and antigens allowing immunity for future infection.
• Vaccines: Dead or weakened pathogens, stimulate the immune system to produce antibodies.
• Antibiotics kill bacteria, not viruses- Penicillin was the first
• Antibiotics increasingly ineffective due to bacterial resistance.

Drug Development

• Historically from plants and organisms.
• Drugs undergo trials
  • Lab trials (cell tissue)
  • Animal trials
  • Human trials
• Placebo studies determine drug effectiveness (blind and double-blind trials minimize bias).

Monoclonal Antibodies (Triple Only)

• Monoclonal antibodies are clones of cells designed to make specific antibodies to combat specific diseases.
• Produced by fusing lymphocytes from mice with tumor cells to create rapidly producing hybrid cells
• Can diagnose medical conditions as well as treat them.
• Can even identify molecules in tissue and bind to them with dyes for examination.
• Side effects are increasingly severe.

Photosynthesis

• Photosynthesis is where chlorophyll and chloroplasts in plant cells provide plants with food.
• The chemical equation of photosynthesis is: 6CO2 + 6H2O -> C6H12O6 + 6O2
• This is an endothermic reaction.
• Glucose is used for respiration, starch/fat storage, cell wall production (cellulose), and protein synthesis (amino acids).
• Factors increasing photosynthesis rate:
  • Higher temperature (up to a point).
  • Increased light intensity.
  • Increased carbon dioxide concentration.

Rate Limiting Factors

• Rates of Photosynthesis limited by any single factor in short supply.
• A graph of photosynthesis rate plateaus when a factor stops limiting.
• The limiting factor can be identified by the variable on the x-axis as the graph plateaus

Photosynthesis Experiment

• Rate of photosynthesis can be measured by the amount of oxygen made.
• Pondweed releases oxygen into an inverted measuring cylinder when submerged
• Bubble counting can be used but is inaccurate.
• Independent variable is light intensity at different distances.
• Light intensity relates to distance in an inverse square fashion

Respiration

• Respiration provides energy for all organisms.
• Aerobic respiration: Requires oxygen: C6H12O6 + 6O2 -> 6CO2 + 6H2O
• Breathing rate and heart rate increase during exercise.
• Anaerobic respiration: Occurs without oxygen and happens when exercising strenuously.
• Glucose is created straight to lactic acid and releases less energy.
• Oxygen debt is created and lactic acid is broken down in the liver, back into glucose.
• Plant and yeast cells can respire anaerobically.
• Anaerobic respiration releases ethanol and Carbon Dioxide in plant and yeast cells (fermentation).

Metabolism

• Metabolism: Sum of all reactions in a cell or organism.

Metabolic Processes

• Glucose to starch, glycogen, and cellulose
• The use of Glucose and nitrates to make Amino Acids for protein synthesis
• Fatty Acids and glycerol can make Lipids
• Breakdown of excess proteins into urea