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

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

Understanding Feeding and Nutrition

Feeding vs. Nutrition: Key Differences

• Feeding (Eating): Subjective, voluntary, and conscious actions related to consuming food.
• Nutrition (Nourishing): Involuntary, unconscious, and objective processes involving the assimilation of nutrients by the body.

Essential Nutrients: Organic and Inorganic

Nutrients are classified based on whether they contain carbon (C).

Inorganic Nutrients

These nutrients do not contain carbon (C). They are vital for bodily functions.

• Water: Essential for all chemical reactions in the body.
• Mineral Salts: Essential inorganic nutrients needed in small amounts.

Organic Nutrients

These nutrients contain carbon (C). They provide energy and building blocks for the body.

• Carbohydrates: Provide fast

Bone Lesions

Cemento-ossifying Fibroma

• Masses of poorly cellular cementum
• Fibro-cellular connective tissue

Central Giant Cell Lesion

• Multinucleated giant cells
• Areas of hemorrhage
• Loose vascular connective tissue rich in mononuclear cells

Facial Fibrous Dysplasia: Osseous Stage

• Dysplastic fibrous tissue
• Trabeculae of woven bone without peripheral osteoblastic rimming
• Trabeculae are equidistant from each other, taking the shape of C, U, or W letters (Chinese letter appearance)
• Retraction of dysplastic fibrous tissue from woven bone trabeculae
• Presence of blood vessels

Facial Fibrous Dysplasia: Osteoid Stage

• Trabeculae of osteoid bone laid down equidistant from each other
• Characteristic C, U, or W letter shapes and Chinese letter appearance

Malignant Neoplasms

Fibrosarcoma

• Malignant

Understanding Coronaviruses

A coronavirus is not just one single bug; it is actually a large family of viruses. They get their name because under a microscope, they look like they are wearing a spiked crown—"corona" means crown in Latin. While many coronaviruses only cause mild illnesses like the common cold, a few rare types can jump from animals to humans and cause severe respiratory infections.

Key Types of Coronaviruses

Most of the time, humans contract mild "community" coronaviruses that cause basic cold symptoms. However, three major outbreaks have occurred due to more dangerous strains:

• SARS-CoV-2 (COVID-19): First identified in late 2019, this is the highly contagious virus responsible for the global COVID-19 pandemic.
• SARS-CoV (SARS):

Joints: Definition and Classification

A joint, also known as an articulation, is the point where two or more bones meet. Joints allow for movement, flexibility, and support in the skeletal system.

Classification of Joints

Joints can be classified based on their structure and function:

Structural Classification

1. Fibrous Joints: Held together by dense connective tissue (e.g., sutures in the skull).
2. Cartilaginous Joints: Connected by cartilage (e.g., intervertebral discs, symphysis pubis).
3. Synovial Joints: Characterized by a fluid-filled space between bones (e.g., hinge joints like the elbow, ball-and-socket joints like the shoulder).

Functional Classification

1. Synarthroses: Immovable joints (e.g., sutures in the skull).
2. Amphiarthroses: Slightly movable joints

Nervous and Endocrine Systems

The nervous system receives external and internal stimuli, interprets them, and decides an appropriate response. The response is executed by the effector organ or tissue. Nervous tissue is made up of cells called neurons.

Stimulus → Nervous System → Effectors → Muscles, Glands

Neuron Structure

• Cell body: The central part of the neuron.
• Dendrites: Extensions of the cell body. They receive the nerve impulse and transmit it to the cell body.
• Axon: A long fiber extending from the cell body. It transmits the nerve impulse to other neurons or effector cells.
• Myelin sheath: This layer protects the axon and increases the speed of the nerve impulse.
• Axon terminals: These are located at the end of the axon. They contain neurotransmitters,

1. Characteristics of Blood Vessels

1. Direction of flow:
   • Arteries: Away from the heart
   • Veins: Towards the heart
   • Capillaries: Between arteries and veins
2. Presence of valves:
   • Arteries: Absent
   • Veins: Present
   • Capillaries: Absent
3. Thickness of walls:
   • Arteries: Thick
   • Veins: Thin
   • Capillaries: Very thin
4. Pressure of blood flowing inside:
   • Arteries: High
   • Veins: Low
   • Capillaries: Low
5. Exchange of materials:
   • Arteries: Does not take place
   • Veins: Does not take place
   • Capillaries: Takes place

2. Labeling the Parts of the Heart

• A: Left ventricle
• B: Left atrioventricular (Bicuspid) valve
• C: Aortic semilunar valve
• D: Left atrium
• E: Pulmonary veins
• F: Left pulmonary artery
• G: Aorta
• H: Superior vena cava
• J: Pulmonary semilunar valve
• K: Right atrium
• L: Right atrioventricular (Tricuspid) valve
• M: Right

The Neuron and Synaptic Communication

Neurons consist of several key components:

• Cell Body (Soma): Houses the nucleus, mitochondria, and DNA; controls cell activities.
• Dendrites: Branching extensions that receive electrical signals and transmit them to the soma.
• Axon: Extends from the cell body to carry electrical signals to other neurons, muscles, or glands.

Synapses

A synapse is the junction where a neuron connects with another cell to send signals.

• Electrical Synapses: Connected by gap junctions allowing direct cytoplasmic continuity. Ions flow directly, making them very fast and often bidirectional; ideal for quick communication in large groups of cells.
• Chemical Synapses: Separated by a tiny gap (the synaptic cleft). They release neurotransmitters

Essential Concepts in Muscle Physiology

Skeletal Muscle Anatomy: The Sarcomere

8. A sarcomere (The basic contractile unit)
9. Myofibril (A bundle of myofilaments)
10. T-tubule; terminal cistern (Components of the Triad)

Sarcomere Components Defined

29. Thin filaments
30. I band: (Light band containing only thin filaments; spans from the Z line into the sarcomere.)
31. Z line: (Anchors thin filaments and defines the boundary of a sarcomere.)
32. H band: (Central part of the A band where only thick filaments are present—no overlap with thin filaments.)
33. M line: (The center of the sarcomere, within the H zone, where thick filaments are linked.)

Excitation-Contraction Mechanisms

6. None of these: The correct answer is the Nicotinic ACh receptor, which was not listed.
7. Sarcoplasmic reticulum