Biology

Cell Structure

Types of Cells

• Prokaryotic Cells (Bacteria): No nucleus, single circular DNA, plasmids, smaller and simpler structure.

• Eukaryotic Cells (Animal & Plant Cells): Nucleus, mitochondria, ribosomes, complex internal structure.

Cell Organelles & Functions

• Nucleus – Contains DNA, controls cell activities.

• Cytoplasm – Site of chemical reactions, contains enzymes.

• Cell Membrane – Controls what enters/leaves the cell, semi-permeable.

• Mitochondria – Site of respiration, energy release (ATP production).

• Ribosomes – Protein synthesis; found on rough ER or floating in cytoplasm.

• Cell Wall (Plant/Bacteria) – Provides structural support, made of cellulose in plants.

• Chloroplasts (Plant) – Photosynthesis occurs here; contains chlorophyll.

• Vacuole (Plant) – Stores cell sap (water, nutrients, waste), maintains cell structure.

Microscopy

• Light Microscope – Uses light, lower resolution (200nm), magnification up to x1500.

• Electron Microscope – Uses electrons, higher resolution (0.2nm), magnification up to x2,000,000.

• Magnification Formula: Image Size = Actual Size × Magnification.

Cell Division

Mitosis (Growth & Repair)

• DNA replicates. (Prophase)

• Chromosomes align in the center. (Metaphase)

• Chromosomes pulled apart. (Anaphase)

• Two identical daughter cells form. (Telophase)

Stem Cells

• Embryonic Stem Cells – Can develop into any cell type.

• Adult Stem Cells – Limited to certain tissues.

• Uses – Treat diseases (e.g., diabetes, paralysis).

• Ethical Issues – Embryo destruction.

Transport in Cells

Diffusion

• Net movement of molecules from high to low concentration.

• Examples: Oxygen & carbon dioxide in lungs.

Osmosis

• Diffusion of water across a partially permeable membrane.

• Hypotonic Solution: Water moves into the cell.

• Hypertonic Solution: Water moves out of the cell.

Active Transport

• Movement of substances against concentration gradient.

• Requires energy (ATP from respiration).

The Heart and Blood Vessels

Blood Vessels

• Arteries – Carry blood away from the heart; thick, muscular walls to withstand high pressure.

• Veins – Carry blood to the heart; thinner walls, valves prevent backflow.

• Capillaries – One cell thick, allow exchange of gases & nutrients between blood and tissues

Heart Structure

• Four Chambers: Left & Right Atrium, Left & Right Ventricle.

• Valves – Prevent backflow of blood.

• Coronary Arteries – Supply oxygen-rich blood to the heart muscle.

• Pacemaker (Sinoatrial Node) – Controls heart rate through electrical impulses.

Cycle of Blood Through the Heart

1. Deoxygenated blood enters the right atrium from the body via the vena cava.

2. Blood moves into the right ventricle and is pumped to the lungs via the pulmonary artery.

3. In the lungs, blood picks up oxygen and releases carbon dioxide.

4. Oxygenated blood returns to the left atrium via the pulmonary vein.

5. Blood moves into the left ventricle, which pumps it around the body via the aorta.

6. Oxygen is delivered to body tissues, and deoxygenated blood returns to the heart to repeat the cycle.

Blood

Components of Blood

• Red Blood Cells – Transport oxygen via hemoglobin.

- Biconcave shape increases surface area.

- No nucleus to allow more room for oxygen.

- Hemoglobin binds to oxygen in the lungs to form oxyhemoglobin and releases oxygen to tissues.

• White Blood Cells – Fight infections...

- By surrounding them and breaking them down with enzymes (phagocytosis).

- By producing antibodies that target pathogens by binding to antigens for destruction.

- By produce antitoxins that neutralize toxins released by bacteria.

• Platelets – Help blood clot.

- Small cell fragments that form clots to stop bleeding and prevent pathogen entry.

• Plasma – Transports substances.

- Carries nutrients (glucose, amino acids), hormones, carbon dioxide, urea, and antibodies throughout the body.