Notes, summaries, assignments, exams, and problems for Biology

Animal Classification

Vertebrates: Possess an endoskeleton and belong to the phylum Chordata. They are divided into 5 main groups:

• Mammalia (Mammals)
• Aves (Birds)
• Reptilia (Reptiles)
• Amphibia (Amphibians)
• Pisces (Fish)

Invertebrates: Often possess an exoskeleton or lack a backbone. Examples include:

• Cnidarians (e.g., jellyfish)
• Arthropods (e.g., insects, spiders)
• Molluscs (e.g., snails, clams)
• Worms (various phyla)

Kingdom Monera

Monera: Consists of prokaryotes (organisms lacking a true nucleus).

Plant Biology Basics

Vascularity refers to whether plants have specialized tissues (veins) for transporting water and nutrients.

• Xylem: Transports water and minerals upwards from the roots.
• Phloem: Carries glucose (food produced during photosynthesis) around the plant.

Week 1: The Heart

Purpose of the Cardiovascular System

To provide adequate blood flow to all tissues/organs according to immediate needs.

Heart Contractions

• Systole: Periods of contraction
• Diastole: Periods of relaxation

Note: The atria contract simultaneously, followed by simultaneous ventricular contraction.

Blood Vessels

• Arteries: Carry blood away from the heart.
• Veins: Carry blood towards the heart.

Intrinsic Conduction System

1. Sinoatrial (SA) Node (Pacemaker): Generates impulses in the right atrial wall. Depolarizes 80-100 times per minute, modified by the autonomic nervous system to approximately 75 times per minute.
2. Atrioventricular (AV) Node: Impulses pause here for 0.1 seconds, allowing the atria to complete contraction. Generates impulses 40-60

The Excretory System

The excretory system is responsible for eliminating waste substances from the body. The main organs involved are:

• The kidneys: They filter the blood and produce urine.
• The lungs: They eliminate carbon dioxide (CO2).
• The liver: It processes bilirubin (a product of red blood cell breakdown) and excretes it with the feces.
• The sweat glands: They produce sweat to regulate body temperature.

The Urinary System

The urinary system is a key part of the excretory system and is made up of:

• Ureters: Tubes that connect the kidneys to the bladder.
• Urinary bladder: A muscular organ that stores urine.
• Urethra: The tube through which urine leaves the body. In men, the urethra is shared by the urinary and reproductive systems, while in women it is

Cells are open systems – they exchange both matter and energy with their environment.

Cellular Open Systems: Examples of Exchange

• In: Water, oxygen, nutrients, solar energy (in plants)
• Out: Carbon dioxide, waste, thermal energy, kinetic energy

Cellular Needs and Organ System Functions

Surface Area to Volume Ratio (SA:V)

Cells work best with a high SA:V ratio (more membrane per unit of volume).

• Small cells = high SA:V → efficient transport
• Large cells = low SA:V → less efficient

SA:V Ratio Calculation Formulas

• Surface Area of cube:

Lymphocyte Migration and Immune Response

Lymphocytes constantly migrate through the blood and lymph, moving from one lymphoid organ to another. This process:

• Enhances the chance that an antibody will encounter its specific antigen.
• The spleen filters blood, while other lymphoid organs filter lymph.

Phagocytosis: A Non-Specific Innate Immune Response

Phagocytosis is the ingestion of microorganisms or particulate matter by a cell. It is performed by phagocytes, which are certain types of white blood cells or their derivatives.

Actions of Phagocytic Cells

1. Among the granulocytes, neutrophils are the most important phagocytes.
2. Enlarged monocytes transform into wandering macrophages and fixed macrophages.
3. Fixed macrophages are located in selected tissues

Local Inflammation

1. Occurs when bacteria enter a break in the skin.
2. Inflammatory reaction is initiated by nonspecific mechanisms of phagocytosis and complement activation.
3. Complement activation attracts phagocytes to the area.
4. As inflammation progresses, B cells produce antibodies against bacterial antigens.
5. Attachment of antibodies to antigens amplifies nonspecific responses because of complement activation.
6. Promotes phagocytic activity of neutrophils, macrophages, and monocytes (through opsonization).
7. In the inflamed area, leukocytes attach to the surface of endothelial cells.
8. Move by chemotaxis to the inflamed site.

• Neutrophils arrive first, then monocytes, then T cells.
  • Undergo extravasation (the entire process of movement of leukocytes from the bloodstream

Alright, let’s make Cell Structure & Cell Theory feel alive—less textbook, more story 👇

What is a Cell? The Mini City of Life

A cell is the tiniest unit of life—like a mini city that keeps everything running.
Your body isn’t one big thing; it’s a community of trillions of cells, each doing its own job but working together so you can breathe, think, move, and feel.

The Three Fundamental Rules of Cell Theory

Cell theory is basically biology’s ground rules. Three simple but powerful ideas:

1. All Living Things Are Composed of Cells

From a tiny bacterium to a giant banyan tree to you—everything alive is built from cells.
Some organisms have one cell, others have millions or trillions, but no cell = no life.

2. The Cell Is the Basic

1. Homeostasis and Ecology

• 1(a) Maintaining constant internal conditions.
• 1(b) 250 hours.
• 1(c)(i) A.
• 1(c)(ii) Fertilisers from farms run off into rivers. This causes algal growth. Less light penetrates, reducing photosynthesis. Pesticides kill organisms.
• 1(d)(i) Low FSH: eggs do not mature.
• 1(d)(ii) Low LH: no ovulation.
• 1(e)(i) Less water is absorbed into the blood. Water moves by osmosis because water potential remains higher in the blood.
• 1(e)(ii) Mutation. Only resistant bacteria survive. They reproduce and pass on the allele.
• 1(f)(i) Denitrifying bacteria convert nitrate to nitrogen gas. This reduces algal growth, so there is more oxygen in rivers.
• 1(f)(ii) Roots absorb water. More transpiration occurs, leading to slower water flow and less runoff.

Antibody Functions

• Precipitation: Binds to soluble molecules so they become insoluble.
• Neutralization: Binds to and prevents the activity of viruses or toxins.

Fc Region Binding

• Phagocytes: Facilitates opsonization and stimulates cytokine release.
• Complement proteins: Stimulates complement fixation, which triggers MAC formation.

Diversity of Antibodies

• Each person has approximately 10²⁰ antibody molecules with millions of different specificities.
• It is likely that an antibody exists for any antigen a person might encounter.
• Mechanisms of diversity:
  • Genetic recombination: Combinations of hundreds of genes coding for heavy and light chains lead to millions of unique antibodies.
  • Somatic hypermutation: Diversity increases via a high rate of single base pair