GCSE Biology: Cell Structure

• Biology is the study of living organisms and their interactions with each other and the environment.
• GCSE Biology Foundation Tier covers fundamental biological concepts, focusing on accessibility and understanding of core principles.

Cell Biology

• Cells are the basic building blocks of all living organisms.
• Plant and animal cells have different structures and organelles.
• Animal cells typically include a nucleus, cytoplasm, cell membrane, and mitochondria.
• Plant cells have the same organelles, plus a cell wall, chloroplasts, and often a vacuole.

Cell Structure

• The nucleus contains the genetic material (DNA), which controls the cell's activities.
• The cytoplasm is a gel-like substance where most chemical reactions happen.
• The cell membrane controls what enters and exits the cell.
• Mitochondria are the sites of aerobic respiration, providing energy for the cell.
• The cell wall (plant cells) provides support and structure.
• Chloroplasts (plant cells) are the sites of photosynthesis.
• Vacuoles (plant cells) store cell sap and help maintain cell turgor.

Specialised Cells

• Specialised cells are adapted to perform specific functions.
• Examples include red blood cells, nerve cells, and muscle cells.
• Red blood cells transport oxygen, nerve cells transmit electrical signals, and muscle cells facilitate movement.
• Sperm and egg cells are specialised for reproduction.
• Root hair cells (plants) are specialised for absorbing water and nutrients from the soil.

Cell Division

• Cell division is essential for growth, repair, and reproduction.
• Mitosis produces two identical daughter cells for growth and repair.
• Meiosis produces four genetically different daughter cells for sexual reproduction (gametes).
• Understanding the stages of mitosis is important: prophase, metaphase, anaphase, and telophase.

Microscopy

• Microscopes are used to observe cells and tissues.
• Light microscopes use light and lenses to magnify images.
• Electron microscopes use electrons to achieve higher magnification and resolution.
• Magnification is the number of times larger an image appears compared to the actual size of the object.

Organisation

• Cells are organised into tissues, tissues into organs, and organs into organ systems.
• Examples of tissues include muscle tissue, nervous tissue, and epithelial tissue.
• Examples of organs include the heart, lungs, and stomach.
• Organ systems work together to perform specific functions, such as the digestive system or the respiratory system.

Enzymes

• Enzymes are biological catalysts that speed up chemical reactions in living organisms.
• Enzymes have a specific shape that allows them to bind to a specific substrate.
• The active site of an enzyme is where the substrate binds and the reaction occurs.
• Enzymes are affected by temperature and pH.
• Optimum temperature and pH are where the enzyme works most effectively.
• Denaturing occurs when the enzyme's shape is changed due to extreme temperature or pH, preventing it from functioning.

Digestion

• Digestion is the breakdown of large, insoluble food molecules into smaller, soluble ones.
• Enzymes play a crucial role in breaking down carbohydrates, proteins, and fats.
• Amylase breaks down starch into sugars.
• Protease breaks down proteins into amino acids.
• Lipase breaks down fats into fatty acids and glycerol.
• The digestive system includes the mouth, oesophagus, stomach, small intestine, large intestine, rectum, and anus.
• Absorption of nutrients mainly occurs in the small intestine.

Plant Nutrition

• Plants require essential nutrients for growth and development.
• Nutrients are absorbed from the soil through the roots.
• Key nutrients include nitrates (for protein synthesis), phosphates (for DNA and cell membranes), and potassium (for enzyme activity).
• A deficiency in these nutrients can lead to stunted growth and other health problems.

Gas Exchange

• Gas exchange is the process by which oxygen and carbon dioxide are exchanged between an organism and its environment.
• In humans, gas exchange occurs in the lungs, specifically in the alveoli.
• Alveoli have a large surface area and thin walls to facilitate diffusion.
• Ventilation (breathing) brings air into and out of the lungs.

Respiration

• Respiration is the process by which energy is released from glucose in the presence or absence of oxygen.
• Aerobic respiration requires oxygen and produces carbon dioxide, water, and a large amount of ATP (energy).
• Anaerobic respiration occurs without oxygen and produces lactic acid (in animals) or ethanol and carbon dioxide (in plants and yeast), yielding less ATP.
• The equation for aerobic respiration is: glucose + oxygen → carbon dioxide + water.
• The equation for anaerobic respiration (in muscles) is: glucose → lactic acid.

Photosynthesis

• Photosynthesis is the process by which plants convert light energy into chemical energy in the form of glucose.
• Chlorophyll, found in chloroplasts, absorbs light energy.
• The equation for photosynthesis is: carbon dioxide + water → glucose + oxygen.
• Factors affecting photosynthesis include light intensity, carbon dioxide concentration, and temperature.
• Photosynthesis is essential for producing oxygen and glucose, which are vital for life on Earth.

Transport in Plants

• Plants transport water and nutrients through vascular tissues: xylem and phloem.
• Xylem transports water and minerals from the roots to the leaves.
• Phloem transports sugars (produced during photosynthesis) from the leaves to other parts of the plant.
• Transpiration is the process of water moving through a plant and evaporating from its leaves.
• Transpiration helps to cool the plant and transport minerals.

Human Transport System

• The human transport system (circulatory system) includes the heart, blood vessels, and blood.
• The heart pumps blood around the body.
• Blood vessels include arteries, veins, and capillaries.
• Arteries carry blood away from the heart, veins carry blood back to the heart, and capillaries facilitate exchange of substances between blood and tissues.
• Blood consists of red blood cells (carry oxygen), white blood cells (fight infection), platelets (help blood clot), and plasma (liquid component).

Homeostasis

• Homeostasis is the maintenance of a stable internal environment.
• This includes regulating body temperature, blood glucose levels, and water balance.
• Control systems involve receptors, coordination centres (e.g., brain), and effectors.
• Negative feedback mechanisms help maintain balance by reversing changes.

Nervous System

• The nervous system enables rapid communication between different parts of the body.
• It consists of the central nervous system (brain and spinal cord) and the peripheral nervous system.
• Neurons (nerve cells) transmit electrical signals called impulses.
• Synapses are junctions between neurons where chemical neurotransmitters transmit signals.
• Reflex actions are automatic and rapid responses to stimuli.

Hormonal Control

• Hormones are chemical messengers produced by endocrine glands.
• Hormones travel in the bloodstream to target organs, where they elicit a response.
• Insulin (produced by the pancreas) regulates blood glucose levels.
• Adrenaline (produced by the adrenal glands) prepares the body for fight or flight.

Reproduction

• Sexual reproduction involves the fusion of gametes (sperm and egg) to produce offspring.
• Asexual reproduction involves only one parent and produces genetically identical offspring.
• Meiosis is the type of cell division that produces gametes.
• Fertilisation is the fusion of a sperm and an egg cell.
• The menstrual cycle in females involves the preparation of the uterus for pregnancy.

Variation and Inheritance

• Variation refers to differences between individuals within a population.
• Genetic variation is caused by differences in genes.
• Inheritance is the passing on of traits from parents to offspring.
• Genes are located on chromosomes and control specific traits.
• Alleles are different forms of a gene.
• Dominant alleles are expressed even if only one copy is present, while recessive alleles are only expressed if two copies are present.

Evolution

• Evolution is the gradual change in the characteristics of a species over time.
• Natural selection is the process by which individuals with advantageous traits are more likely to survive and reproduce.
• Evidence for evolution includes fossils, comparative anatomy, and DNA analysis.

Ecology

• Ecology is the study of the interactions between organisms and their environment.
• Ecosystems include all the living organisms (biotic factors) and non-living components (abiotic factors) in a particular area.
• Food chains and food webs show the flow of energy through an ecosystem.
• Producers (plants) are at the bottom of the food chain, followed by consumers (animals).
• Decomposers break down dead organisms and recycle nutrients.

Biodiversity

• Biodiversity refers to the variety of life on Earth.
• Maintaining biodiversity is important for ecosystem stability and human well-being.
• Threats to biodiversity include habitat destruction, pollution, climate change, and overexploitation of resources.
• Conservation efforts aim to protect and restore biodiversity.