Igcse biology

• Cellular respiration occurs inside cells, specifically within mitochondria.
• The process by which the body uses glucose to produce energy is called cellular respiration.
• Glycolysis is anaerobic (does not require oxygen) and takes place in the cytoplasm of all living organisms.
• Glycolysis is anaerobic (does not require oxygen) and takes place in the cytoplasm of all living organisms.
• The process involves the breakdown of glucose to release energy that is used by the cell.
• The process involves the breakdown of glucose to release energy that is used by the cell.
• Characteristics of living organisms:

  • Movement: Living organisms can move all or part of themselves. Animals move to find food or escape predators, while plants move their leaves to catch sunlight
  • Respiration: Series of chemical reactions in cells breaking down nutrient molecules to release energy for metabolism
  • Sensitivity: Living organisms can detect changes in their internal or external environments and respond to these changes
  • Growth: Organisms grow, leading to a permanent increase in size, measured through dry mass, cell size, or number of cells
• • Reproduction: Living organisms reproduce to create more organisms of their kind
  • Excretion: Removal of waste products from metabolic reactions, including toxic materials, excess substances, and carbon dioxide from respiration
  • Nutrition: Organisms take in materials for development and use them in chemical reactions to produce energy for growth and repair
• Viruses are not classified as living as they do not complete the processes mentioned. They are non-cellular and consist of genetic material surrounded by a protein coat. When they reach a target cell, they inject genetic material for reproduction, harming the target cell
• Classification:

  • Organisms belong to the same species if they can reproduce to produce fertile offspring
  • Organisms are classified by evolutionary relationships found through physical characteristics and DNA base sequences
  • Traditionally, organisms were categorized based on morphology and anatomy
  • DNA sequencing studies allow for mapping and comparing DNA of different species, leading to more accurate classification
  • Organisms are named using the binomial naming system with Latin names consisting of two words, referring to genus and species
• The five kingdoms are Animal, Plant, Fungus, Prokaryote, and Protoctista

  • Features of cells help categorize organisms into these kingdoms
  • Animal cells lack a cell wall and chlorophyll, unlike plant cells
• Features of cells:

  • Cytoplasm: Jelly-like material within the cell where reactions occur, containing organelles like the nucleus and ribosomes
  • Cell membrane: Thin membrane surrounding the cell, controlling entry and exit of substances
  • DNA: Genetic material in the nucleus coding for proteins
  • Ribosomes: Site of protein synthesis
  • Enzymes: Catalyze reactions such as respiration in the cell
• Within the animal kingdom, organisms are further categorized into vertebrates and arthropods

  • Vertebrates have a backbone, including mammals, birds, reptiles, amphibians, and fish
  • Arthropods lack a backbone and are identified by their exoskeleton and segmented body, including myriapods, insects, arachnids, and crustaceans
• The plant kingdom is split into flowering and non-flowering plants

  • Flowering plants are divided into dicotyledons and monocotyledons, identified by their leaves
  • Non-flowering plants like ferns reproduce through spores instead of producing seeds
• Cells can be viewed using a microscope to study their structure
• Plant and animal cells are known as eukaryotic cells as they contain a nucleus and membrane-bound organelles such as ribosomes and mitochondria
• Bacteria are known as prokaryotes as they do not contain a nucleus and membrane-bound organelles like eukaryotic cells
• To calculate the size of a specimen under a microscope, the image size is the size the specimen appears when viewed through the microscope
• • Vesicles: Used to transport materials in the cell
• Functions of eukaryotic cell structures:

  • Cytoplasm: A jelly-like material within the cell where reactions occur, containing structures like ribosomes and vesicles
  • Cell membrane: A thin membrane surrounding the cell, controlling entry and exit of substances
  • Nucleus and DNA: Nucleus contains genetic material (DNA) which codes for proteins, and DNA replication occurs in the nucleus
  • Ribosomes and rough endoplasmic reticulum (RER): RER surrounds the nucleus and ribosomes are attached to it, site of protein synthesis
  • Mitochondria: Site of respiration, providing energy for the cell
• In addition to the above, plant cells also contain a vacuole, chloroplasts, and are surrounded by a cell wall

  • Vacuole: Fluid-filled sac containing mineral salts, sugars, amino acids, waste substances, and pigments
  • Chloroplasts: Site of photosynthesis, converting light energy to glucose
  • Cell wall: Provides structure, prevents bursting, controls what enters and exits the cell
• Levels of organisation:

  • Tissue: Group of similar cells working together to carry out a particular process
  • Organ: Group of tissues working together to carry out a specific function
  • Organ system: Group of related organs working together to carry out functions in the body
• Specialised cells:

  • Ciliated cells: Found lining the trachea, have cilia to transport mucus, dust, and bacteria upwards
  • Root hair cells: Adapted for a large surface area to speed up osmosis and mineral ion uptake in plants
  • Xylem vessels: Used to transport water through plants in transpiration, made from hollowed-out dead cells with thick cell walls for structural strength and thin to allow capillary action
  • Palisade mesophyll cells: Efficiently absorb light with lots of chloroplasts for photosynthesis, placed at the top of the leaf to absorb light energy
• • Nerve cells: Adapted to transmit electrical impulses rapidly, myelinated for insulation, contain lots of mitochondria for energy, dendrites have a large surface area and are branched to receive impulses
  • Red blood cells: Contain haemoglobin to carry oxygen, biconcave shape for increased surface area, thin cell membranes for rapid diffusion, do not contain a nucleus to have more space for oxygen
  • Sperm cells: Contain lots of mitochondria for energy, have a tail for movement, and digestive enzymes to penetrate the egg cell membrane
• The cell membrane and cell wall control what substances enter and exit the cell
• Molecules like glucose and proteins move into the cell for metabolic reactions and storage
• Waste products such as carbon dioxide and lactic acid are transported out into the blood to be excreted from the body
• Diffusion is the net movement of particles from an area of high concentration to an area of low concentration down the concentration gradient
• Energy for diffusion comes from the kinetic energy of the molecules
• Solutes and gases like carbon dioxide and oxygen can diffuse in and out of cells across the cell membrane
• Factors affecting rate of diffusion:

  • Surface area: as it increases, the rate of diffusion increases
  • Temperature: as it increases, the rate of diffusion increases
  • Concentration gradient: as it increases, the rate of diffusion increases
  • Diffusion distance: a greater diffusion distance slows the rate of diffusion
• Osmosis is the net movement of water molecules through a partially permeable membrane
• Key terms:

  • Turgid: cells are swollen due to high-water content
  • Turgor pressure: pressure on the cell wall from the cell membrane pushing upon it
  • Flaccid: occurs when water moves out of the cell via osmosis
  • Plasmolysis: occurs when there is too little water in cells
• Water moves in and out of cells through the cell membrane via osmosis
• Water provides support for the cell structure through maintaining turgor pressure
• Water acts as a temperature buffer, maintaining the optimum temperature for enzyme reactions
• Water particles diffuse from regions of high-water potential to regions of low water potential
• Active transport is the movement of molecules against a concentration gradient using energy from respiration
• Carrier proteins facilitate active transport by binding molecules from the side with lower concentration and changing shape using energy from respiration
• Examples of active transport:

  • Uptake of ions by root hair cells
  • Uptake of glucose in the small intestine and kidney tubules