Cell Biology and Organization

Cells are the fundamental units of life, categorized into animal and plant cells with distinct structures. Organisms exhibit a hierarchical organization from cells to complex systems.

Animal Cells: Possess a cell membrane, cytoplasm, nucleus, mitochondria, and small vacuoles.
Plant Cells: Feature a cell wall, cell membrane, cytoplasm, nucleus, mitochondria, chloroplasts, and a large central vacuole.
Levels of Organization: Progress from cells to tissues, organs, organ systems, and finally, the complete organism.

Transport Across Membranes

Substances move in and out of cells through processes like diffusion and osmosis, crucial for maintaining cellular function.

Diffusion: The net movement of particles from an area of higher concentration to an area of lower concentration.
Osmosis: The net movement of water molecules across a partially permeable membrane from a region of higher water potential to one of lower water potential.
Cellular Effects: Animal cells may lyse or crenate, while plant cells become turgid or plasmolyzed depending on water potential.

Energy and Life Processes

Photosynthesis and respiration are vital processes for energy capture and release in living organisms.

Photosynthesis: Plants convert light energy, carbon dioxide, and water into glucose and oxygen (6CO₂ + 6H₂O + Light → C₆H₁₂O₆ + 6O₂).
Aerobic Respiration: Organisms break down glucose with oxygen to release energy, carbon dioxide, and water (C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy).
Anaerobic Respiration: Releases less energy without oxygen, producing lactic acid in animals or ethanol and carbon dioxide in yeast.

Digestion and Enzymes

The digestive system breaks down food into absorbable nutrients, facilitated by specialized biological catalysts called enzymes.

Digestive System: Involves organs like the mouth, esophagus, stomach, small intestine, and large intestine, each with specific roles in mechanical and chemical digestion.
Enzymes: Biological catalysts that speed up biochemical reactions, exhibiting specificity (lock and key model) and optimal activity at specific temperatures and pH levels.
Denaturation: Extreme conditions can alter enzyme structure, leading to a loss of function.

Circulation and Respiration Systems

These systems work in tandem to transport essential substances and facilitate gas exchange throughout the body.

Circulatory System: Comprises the heart, blood vessels (arteries, veins, capillaries), and blood, responsible for transporting oxygen, nutrients, and waste.
Respiratory System: Involves organs like the trachea, bronchi, and lungs, facilitating the exchange of oxygen and carbon dioxide in the alveoli.
Gas Exchange: Occurs across the thin walls of alveoli, driven by concentration gradients.

Excretion and Control Systems

The body removes waste products and coordinates internal functions through the excretory, nervous, and endocrine systems.

Excretory System: Primarily the kidneys, which filter blood to produce urine, removing waste products like urea.
Nervous System: Consists of the brain, spinal cord, and nerves, coordinating rapid responses through electrical impulses via neurons and reflex arcs.
Endocrine System: Glands secrete hormones (chemical messengers) into the bloodstream to regulate slower, long-term processes like growth and metabolism.

Reproduction and Genetics

Reproduction ensures species continuity, while genetics explains the inheritance of traits.

Reproduction: Can be asexual (one parent, identical offspring) or sexual (two parents, varied offspring).
Human Reproduction: Involves male and female reproductive organs, leading to fertilization and development.
Genetics: Studies heredity, involving chromosomes, genes (segments of DNA), alleles (different gene forms), genotypes (genetic makeup), and phenotypes (observable traits).

Ecology and Environmental Impact

Ecology examines interactions within ecosystems, and human activities significantly impact these natural balances.

Ecology: The study of organisms and their interactions with each other and their environment, including biotic (living) and abiotic (non-living) components.
Food Chains/Webs: Illustrate energy flow through trophic levels, with only about 10% of energy transferred at each step.
Human Impact: Activities like deforestation, pollution, and global warming pose significant threats to ecosystems and biodiversity, necessitating conservation efforts.

Lower Secondary Science Overview: Key Concepts

Lower Secondary Science Overview: Key Concepts