Biology_O_Level

Biology O Level Cambridge 2024-2025

Contents Overview

Number Of Chapters:

1. Characteristics & Classification of Living Organisms

2. Cells

3. Movement into and out of Cells

4. Biological Molecules

5. Enzymes

6. Plant Nutrition

7. Human Nutrition

8. Transport in Plants

9. Transport in Animals

10. Diseases and Immunity

11. Respiration and Gas Exchange

12. Coordination and Response

13. Excretion and Homeostasis

14. Reproduction in Plants

15. Reproduction in Humans

16. Chromosomes, Genes, and Proteins

17. Variation and Selection

18. Biotechnology and Genetics

19. Organisms and Their Environment

20. Human Influences on Ecosystems

Chapter 1: Characteristics and Classification of Living Organisms

A. Characteristics of All Living Organisms

• MRS GREN: This acronym summarizes the seven vital functions of life:

  • Movement: Change in position or location relative to the environment. This can occur both externally (e.g., locomotion) and internally (e.g., the movement of substances within an organism).

  • Respiration: The biochemical process through which cells convert glucose and oxygen into energy (ATP), releasing carbon dioxide and water as byproducts. This process can be aerobic (with oxygen) or anaerobic (without oxygen).

  • Sensitivity: The ability of organisms to perceive and respond to stimuli in their environment, crucial for survival and interaction with other organisms.

  • Growth: The irreversible increase in size and mass, typically involving cell division and differentiation.

  • Reproduction: The biological process by which new individual organisms are produced, ensuring the continuation of species. This can occur sexually or asexually.

  • Excretion: The removal of metabolic waste products from the body, which is vital for maintaining homeostasis.

  • Nutrition: The process of obtaining and using nutrients and energy from food, essential for growth, repair, and maintaining vital functions.

B. Characteristics of Some Living Organisms

• Breathing: The process of intake of oxygen and expulsion of carbon dioxide, particularly in animals with lungs, playing a key role in respiration.

• Development: Refers to the process where organisms undergo changes and increase in complexity during their life cycle, often involving differentiation of cells.

• Egestion: The process of discharging undigested food from the body, distinct from excretion, which deals with metabolic waste.

Classification of Living Organisms

• Species Definition: A group of organisms that can interbreed to produce fertile offspring. Species serve as the basic unit of classification in biology.

• Binomial System: A standardized naming system (developed by Carl Linnaeus) that assigns each organism a two-part Latin name: the genus name (capitalized) and the species name (lowercase). For example, the domestic cat is named Felis catus.

• Dichotomous Key: A decision-making tool that assists in identifying organisms based on contrasting characteristics, guiding the user through a series of choices until the organism is identified.

Five Kingdoms of Life

1. Animals: Multi-cellular, heterotrophic organisms that do not have a cell wall. They typically exhibit complex behavior due to advanced nervous systems.

2. Plants: Multi-cellular, autotrophic organisms that possess cell walls made of cellulose, contain chloroplasts for photosynthesis, and do not move.

3. Fungi: Eukaryotic organisms that can be unicellular (yeasts) or multicellular (molds, mushrooms), characterized by a cell wall made of chitin. They primarily serve as decomposers and exhibit a variety of reproductive mechanisms, including spore production.

4. Prokaryotes: Unicellular organisms without a true nucleus, often classified as bacteria. Their genetic material is in a circular form known as plasmids, and they can be both autotrophic or heterotrophic.

5. Protoctists: A diverse group of organisms including unicellular and simple multicellular forms; some contain chloroplasts, while others do not. They are often classified based on their mode of nutrition, reproduction, and habitat.

Animal Kingdom Groups

• Vertebrates: Animals with a backbone, further classified into five groups: Mammals, Fish, Birds, Reptiles, and Amphibians.

• Invertebrates: Animals without backbones, exhibiting a vast range of forms and behaviors.

Classification of Vertebrates

• Fish: Aquatic animals characterized by scales and gills for respiration.

• Amphibians: Animals that typically have a life stage in water (tadpole) and later on land (frog), able to breathe through skin and lungs.

• Reptiles: Cold-blooded vertebrates with scales, laying eggs with leathery shells.

• Birds: Warm-blooded vertebrates with feathers, lightweight bones, and lungs adapted for efficient respiration.

• Mammals: Warm-blooded vertebrates characterized by hair or fur, mammary glands for nursing young, and advanced brain functions.

Non-Flowering vs Flowering Plants

• Ferns: Non-flowering plants that reproduce using spores produced on the undersides of fronds.

• Flowering Plants: Characterized by reproductive structures known as flowers, with seeds developing in fruits; further classified into monocots (one cotyledon) and dicots (two cotyledons).

Viruses

• Classification: Viruses are not classified within the five kingdoms due to their unique structure, which consists of a core of genetic material (DNA or RNA) encased in a protein coat. Viruses require a host cell to replicate and do not carry out metabolic processes independently.

Questions and Answers (Example)

1. Yaks belong to genus Bos and species Bos grunniens.

2. Staphylococcus aureus belongs to genus Staphylococcus and the prokaryote kingdom.

3. Amphibians have smooth skin for moisture absorption, while reptiles are equipped with scales to prevent water loss.

4. External features of mammals include hair, external ears (pinnae), and mammary glands.

Chapter 2: Cells

Types of Cells:

• Animal Cells

• Plant Cells

• Bacterial Cells

• Specialized Cells

Definitions

• Cell: The basic and smallest unit of life that can replicate independently.

• Tissues: Groups of similar cells that work together to perform a specific function.

• Organs: Structures composed of different types of tissues that perform specific functions within an organism.

• Organ Systems: Complex structures formed by multiple organs that work together to carry out a particular function in the body.

Advanced Cell Structure Overview

• Comparison of Animal & Plant Cells, detailing structural components and their functions, notably cell walls (in plants) and chloroplasts (in plants).

Cell Comparison

Cell Organelles Function

• Cell Membrane: Semi-permeable barrier that regulates entry and exit of substances.

• Nucleus: Contains genetic material (DNA) and controls cellular activities through gene expression.

• Cytoplasm: Site for metabolic activity, hosting organelles and cellular components.

• Mitochondria: Powerhouse of the cell, where aerobic respiration occurs, producing ATP.

• Ribosomes: Sites of protein synthesis, translating mRNA into polypeptides.

Plant Cell Organelles Specifics

• Cell Wall: Provides structural support, protection, and shape to the plant cell.

• Chloroplasts: Organelles where photosynthesis occurs, converting sunlight into chemical energy (glucose) using CO2 and H2O.

• Vacuoles: Large organelles in plant cells for storage of substances (such as water, nutrients), maintaining turgor pressure and cell structure.

Bacterial Cells Overview

• Unicellular organisms without a nucleus and possessing unique genetic organization, such as circular DNA and plasmids that can confer advantageous traits (e.g., antibiotic resistance).

Specialized Cells in Animals

• Ciliated Cells: Facilitate movement of mucus in the respiratory tract, helping to trap and expel pathogens.

• Neurons: Specialized for transmitting signals throughout the body, functioning in communication between body parts.

• Red Blood Cells: Specialized cells mainly responsible for oxygen transport via hemoglobin.

• Gametes (Sperm and Egg Cells): Specialized cells involved in sexual reproduction, contributing genetic material to offspring.

Specialized Cells in Plants

• Root Hair Cells: Adapted for maximum absorption of water and minerals from the soil through increased surface area.

• Palisade Mesophyll Cells: Located just beneath the leaf surface, packed with chloroplasts for efficient photosynthesis.

Size of Specimens

• Overview of magnification concepts, including the use of microscopes to view cellular structures.

Chapter 3: Movement In and Out of Cells

Passive Transport vs. Active Transport

• Definitions and examples illustrating movement across cell membranes.

Key Definitions

• Diffusion: The passive movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached.

• Osmosis: A specific type of diffusion involving the movement of water molecules across a semi-permeable membrane.

• Active Transport: The process of moving molecules against their concentration gradient, requiring energy (ATP).

Active Transport in Plants

• Example: The process by which root hair cells absorb essential mineral nitrates from the soil against their concentration gradient, critical for plant growth and development.

Biological Processes Overview

• Comparisons of diffusion and active transport characteristics, highlighting their significance in maintaining cellular homeostasis.

Biological Molecules

• In-depth exploration of the composition, structure, and roles of carbohydrates, proteins, lipids, and nucleic acids in biological systems and processes.

Enzymes Overview

• Examining the structure and function of enzymes, their role in catalyzing biochemical reactions, and their importance in processes such as digestion and biotechnology.

Advanced Topics

• Detailed discussions on genetics, variation, biotechnology applications, ecosystem dynamics, population studies, environmental impacts, conservation methods, and human health & disease management, embracing the complexity and interrelatedness of biological phenomena.