Biology Class Notes

Introduction to Biology
Biology is the scientific study of life and living organisms. It is a broad field
encompassing multiple disciplines, including genetics, evolution, cell
biology, physiology, ecology, and microbiology. The study of biology helps
us understand the structure, function, growth, origin, evolution, and
distribution of living things. Scientists use the scientific method to
observe, hypothesize, experiment, and analyze biological phenomena.

Characteristics of Living Organisms

All living organisms share common characteristics that define life:

1. Organization – Living things are made of cells, the basic unit of life.

2. Metabolism – They undergo chemical processes to obtain energy

and sustain life.

3. Homeostasis – They regulate internal conditions to maintain

stability.

4. Growth and Development – Organisms grow and develop

according to genetic instructions.

5. Reproduction – Living things produce offspring to pass on genetic

information.

6. Response to Stimuli – Organisms react to environmental changes.

7. Adaptation and Evolution – Species evolve over time through

natural selection.

Cell Biology
Cells are the fundamental unit of life. There are two major types of cells:

 Prokaryotic cells (e.g., bacteria and archaea) lack a nucleus and

membrane-bound organelles.

 Eukaryotic cells (e.g., plants, animals, fungi, and protists) have a

nucleus and organelles.

Organelles within eukaryotic cells include:

 Nucleus – Stores genetic material (DNA).

 Mitochondria – The powerhouse of the cell; produces energy (ATP)

via cellular respiration.

 Ribosomes – Sites of protein synthesis.

 Endoplasmic Reticulum (ER) – Smooth ER synthesizes lipids;

Rough ER has ribosomes and helps in protein synthesis.
  Golgi Apparatus – Modifies and packages proteins.

 Lysosomes – Contain digestive enzymes to break down waste.

 Chloroplasts (in plants) – Conduct photosynthesis.

 Cell Membrane – Regulates movement of substances in and out of

the cell.

Genetics and Heredity

Genetics is the study of heredity and how traits are passed from parents
to offspring.

 DNA (Deoxyribonucleic Acid) – The molecule that carries genetic

information.

 Genes – Segments of DNA that code for proteins.

 Chromosomes – Structures that contain DNA; humans have 46 (23

pairs).

 Mendelian Genetics – Gregor Mendel’s experiments led to the

discovery of dominant and recessive traits.

 Punnett Squares – A tool to predict genetic crosses.

 Mutations – Changes in DNA that can lead to genetic diversity or

diseases.

Evolution and Natural Selection

Evolution is the process through which species change over time. Charles
Darwin proposed the theory of natural selection:

1. Variation – Individuals in a species vary in traits.

2. Overproduction – More offspring are produced than can survive.

3. Adaptation – Traits that enhance survival are passed down.

4. Descent with Modification – Over generations, favorable traits

become more common.

Evidence for evolution includes fossil records, comparative anatomy,

molecular biology, and biogeography.

Photosynthesis and Cellular Respiration

 Photosynthesis (in plants) converts sunlight into chemical energy:

o Equation: 6CO2 + 6H2O + light → C6H12O6 + 6O2

o Occurs in chloroplasts.
  Cellular Respiration (in plants and animals) releases energy from
glucose:

o Equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP

o Occurs in mitochondria.

Human Body Systems

1. Circulatory System – Transports blood, oxygen, and nutrients

(heart, blood vessels).

2. Respiratory System – Exchanges gases (lungs, trachea).

3. Digestive System – Breaks down food and absorbs nutrients

(stomach, intestines).

4. Nervous System – Controls body functions (brain, spinal cord,

nerves).

5. Skeletal System – Supports and protects organs (bones, cartilage).

6. Muscular System – Enables movement (muscles, tendons).

7. Endocrine System – Regulates hormones (glands, pancreas).

8. Reproductive System – Produces offspring (ovaries, testes).

9. Immune System – Defends against pathogens (white blood cells,

lymph nodes).

Ecology and Ecosystems

Ecology is the study of interactions between organisms and their
environment. Levels of organization:

 Organism – A single living being.

 Population – A group of the same species in an area.

 Community – Different species living together.

 Ecosystem – Communities and their environment.

 Biosphere – All ecosystems on Earth.

Food Chains and Webs:

 Producers (Autotrophs) – Make their own food (plants, algae).

 Consumers (Heterotrophs) – Eat other organisms:

o Primary consumers – Herbivores (eat plants).

o Secondary consumers – Carnivores (eat herbivores).

 o Tertiary consumers – Top predators.

 Decomposers – Break down dead organisms (bacteria, fungi).

Environmental Issues

 Pollution – Harmful substances in air, water, and soil.

 Deforestation – Loss of forests due to human activity.

 Climate Change – Rising global temperatures due to greenhouse

gases.

 Biodiversity Loss – Decline in species due to habitat destruction.

 Conservation Efforts – Recycling, protecting endangered species,

and using renewable energy.

Biotechnology and Its Applications

Biotechnology involves using living organisms to develop products.
Applications include:

 Genetic Engineering – Modifying DNA (e.g., GMOs, gene therapy).

 Cloning – Creating identical copies of organisms.

 CRISPR Technology – Gene-editing tool for disease treatment.

 Stem Cell Research – Studying cells that can develop into different
types.

 Bioremediation – Using microbes to clean environmental pollution.

Conclusion
Biology helps us understand life at various levels, from cells to
ecosystems. It plays a crucial role in medicine, agriculture, environmental
conservation, and technology. As scientific advancements continue,
biology remains an essential field for solving global challenges and
improving human well-being.