IGCSE Biology: Cell Organelles, Cell Types & Genetic Concepts

The text is an IGCSE biology tutorial covering various topics such as the characteristics of living organisms, plant and animal cell organelles, eukaryotes vs. prokaryotes, and different types of cells like bacterial cells.

Living organisms share features like movement, respiration, sensitivity, nutrition, excretion, reproduction, and growth.

Both animal and plant cells share organelles like cell membranes, cytoplasm, nuclei, ribosomes, and mitochondria.

Plant cells have unique organelles like the cell wall, vacuole, and chloroplasts where photosynthesis takes place.

Eukaryotes are animal cells with membrane-bound organelles, while prokaryotes like viruses and bacteria lack membrane-bound organelles and nuclei.

Bacterial cells have a cell wall, slime capsule, flagella for movement, nucleoid instead of a distinct nucleus, plasmids, cytoplasm, and cell membranes.

Bacteria can be pathogenic (e.g., pneumococcus, tuberculosis) or beneficial (e.g., lactobacillus bulgaricus in yogurt).

Viruses are smaller than bacteria, made of protein coat and DNA/RNA, lack organelles, and are always pathogenic (e.g., flu virus, HIV).

Protists are a diverse group with properties of both animal and plant cells (e.g., algae, amoeba), causing diseases like malaria (Plasmodium).

Fungi have cell walls, lack chloroplasts, carry out saprotrophic nutrition by secreting enzymes onto dead matter (e.g., yeast used in beer making).

Carbohydrates are stored as glycogen in animals, starch in plants, and glycogen in fungi.

Organization within organisms progresses from cells to tissues to organs to organ systems to the organism itself.

The digestive system includes organs like the stomach, esophagus, pancreas, small intestine, and large intestine.

Enzymes are biological catalysts with active sites that bind substrates to form enzyme-substrate complexes.

Enzyme activity is influenced by temperature and pH, with optimal conditions varying for different enzymes.

Transport mechanisms in cells include diffusion (high to low concentration), osmosis (water movement), and active transport (low to high concentration).

Photosynthesis occurs in chloroplasts, involving chlorophyll, and the equation is carbon dioxide + water -> glucose + oxygen.

Limiting factors for photosynthesis include carbon dioxide levels, light intensity, and temperature.

Leaf structure adaptations for photosynthesis include a large surface area, thinness for easy gas diffusion, waxy cuticle to prevent water loss, palisade mesophyll for chloroplast-rich photosynthesis, spongy mesophyll with air spaces for gas exchange, and guard cells in the lower epidermis for stomata regulation.- Plant Structures and Functions*

Stomata: Open or close to regulate gas exchange and water loss.

Xylem: Transports water and minerals upwards.

Phloem: Transports sugar and nutrients throughout the plant.

Chloroplasts: Contain chlorophyll, the pigment responsible for photosynthesis.

Transport in Plants*

Water and minerals move upwards through xylem by capillary action and transpiration.

Sugar is transported through phloem by active transport.

Transport in Animals*

Blood: Liquid that transports oxygen, nutrients, hormones, and waste products.

Red blood cells: Contain hemoglobin, which binds to oxygen.

White blood cells: Include phagocytes (engulf pathogens) and lymphocytes (produce antibodies).

Heart: Pumps blood through the circulatory system.

Arteries: Carry blood away from the heart.

Veins: Carry blood back to the heart.

Capillaries: Allow exchange of substances between blood and cells.

Circulatory Systems*

Double circulatory system: Blood passes through the heart twice for every lap around the body, ensuring efficient oxygen delivery.

Immune System*

White blood cells: Protect the body from pathogens (microorganisms that cause disease).

Phagocytes: Engulf and destroy pathogens.

Lymphocytes: Produce antibodies that neutralize specific pathogens.

Hormones and Nervous System*

Hormones: Chemical messengers that travel in the blood to coordinate body functions.

Nervous system: Uses electrical impulses to transmit signals rapidly.

Reflex actions: Involuntary responses to stimuli that do not involve conscious thought.

Skin*

Provides a physical barrier against pathogens and water loss.

Acts as a sense organ for pressure, touch, and pain.

Controls body temperature through sweating and hair.

Homeostasis*

The maintenance of a stable internal environment within the body.

Temperature regulation: Sweating and hair stand up or lie down to adjust body temperature.

Adrenaline: Hormone released in stressful situations, preparing the body for "fight or flight" by increasing heart rate and breathing, diverting blood to muscles, and dilating pupils.

Reproduction*

Sexual reproduction: Involves fusion of gametes (egg and sperm) to form a zygote.

Asexual reproduction: Produces genetically identical offspring without gametes.

Pollination: Transfer of pollen from the anther (male part) to the stigma (female part) of a plant.

Fertilization: Union of sperm and egg to form a zygote.

Human Reproduction*

Male reproductive system: Produces sperm and testosterone.

Female reproductive system: Manufactures eggs, provides nourishment for the developing fetus, and supports childbirth.

Placenta: Supports the growing fetus by providing oxygen, nutrients, and waste removal.

Protein Synthesis*

Genes: Sections of DNA that code for specific proteins.

Genotype: The genetic makeup of an organism.

Phenotype: The physical appearance of an organism.

Homozygous: Having two identical alleles for a gene.

Heterozygous: Having two different alleles for a gene.

Dominant trait: Expressed in an individual with at least one dominant allele.

Recessive trait: Expressed only in individuals with two recessive alleles.

Genetics*

Punnett squares: Used to predict the probability of offspring with specific genotypes and phenotypes.

Pedigree analysis: Used to trace the inheritance of traits through generations.

Evolution and Natural Selection*

Evolution: The change in the genetic makeup of a population over time.

Natural selection: Individuals with traits that make them better adapted to their environment are more likely to survive and reproduce, passing on their favorable genes.

Ecology*

Biotic factors: Living organisms that affect one another.

Abiotic factors: Non-living factors that affect organisms.

Food chain: Represents the flow of energy through a series of organisms, with each organism feeding on the one below it.

Food web: A complex network of interconnected food chains.

Pyramids of biomass: Show the amount of living material at each trophic level in an ecosystem.

Human Impact on the Environment*

Eutrophication: Enrichment of water bodies with nutrients, leading to algal blooms and oxygen depletion.

Greenhouse effect: Enhanced by human activities, causing global warming and its associated impacts (sea level rise, extreme weather, biodiversity loss).

Carbon monoxide: A toxic gas released by car engines, binding to hemoglobin and preventing oxygen transport.

Biological Resources*

Greenhouses: Artificial environments that control environmental factors (temperature, light, carbon dioxide levels) to increase crop yield.

Fertilizers: Replace lost nutrients in soil to enhance plant growth.

Pesticides: Control pests to reduce crop damage.

Biological control: Uses other organisms (e.g., ladybugs) to control pests in a more sustainable way.

Microorganisms: Used in food production (e.g., yeast in bread and beer).- Yogurt making involves the use of the bacterium Lactobacillus bulgaricus, which converts lactose into lactic acid, giving yogurt its distinctive flavor.

A fermenter is a vessel used to contain microorganisms involved in fermentation reactions.

Fermenters are optimized with a cooling jacket to control temperature, pH monitors to ensure the right acidity level, stirring paddles for even distribution of nutrients and heat, and an air inlet for microorganisms that require oxygen.

Selective breeding is a process where animals or plants with desired characteristics are bred over many generations to produce offspring with those traits.

In the dairy industry, dairy cows with high milk yields are selectively bred to produce more milk.

Genetic engineering involves manipulating the genes of organisms to produce desired traits.

Genetic engineering can be used to produce human insulin by inserting the insulin gene into bacterial plasmids, which act as vectors for producing insulin in large quantities.

Plants can also be genetically modified to have specific characteristics, such as frost resistance, extended shelf life, or resistance to herbicides.

Golden Rice is an example of genetically modified rice that contains vitamin A, providing nutritional benefits to people in poorer countries.

Tobacco plants can be modified to produce hepatitis antigens, potentially providing a vaccine against hepatitis.

Transgenic organisms are those that have had a gene from another species inserted into them. An example is goats that have had a spider gene inserted, allowing them to produce spider webs in their milk.