biology igcse cambridge all topics

• Sensitivity


  The ability to detect or sense stimuli in the internal or external environment and to make appropriate responses
• Growth


  A permanent increase in size and dry mass by an increase in cell number or cell size or both
• Excretion


  The removal from organisms of the waste products of metabolism, toxic materials and substances in excess of requirements
• Nutrition


  The taking in of materials for energy, growth and development. Plants require light, carbon dioxide, water and ions. Animals need organic compounds and ions and usually need water
• Autotrophs


  Photosynthetic plants that are usually the first organisms in food chains
• Species


  A group of organisms that can reproduce to produce fertile offspring
• Binomial system


  An internationally agreed system in which the scientific name of an organism is made up of two parts showing the genus and the species
• Organisms can be classified into groups by the features that they share
• Classification systems aim to reflect evolutionary relationships
• Classification is traditionally based on studies of morphology and anatomy
• Binomial system


  The scientific name of an organism is made up of two parts showing the genus and the species
• The sequences of bases in DNA and of amino acids in proteins are used as a more accurate means of classification
• Organisms which share a more recent ancestor have base sequences in DNA that are more similar than those that share only a distant ancestor
• Features in cells of all living organisms

  • Cytoplasm
  • Cell membrane
  • DNA as genetic material
  • Ribosomes for protein synthesis
  • Enzymes involved in respiration
• Five kingdoms of classification

  • Animal
  • Plant
  • Fungus
  • Prokaryote
  • Protoctist
• Animals


  • Multicellular organisms whose cells have no cell walls or chloroplasts
  • Most animals ingest solid food and digest it internally
• Arthropods


  • Jointed limbs
  • Hard, firm external skeleton called a cuticle
  • Segmented bodies with flexible joints between segments
  • Distinct head, thorax and abdomen regions
• Crustacea


  • Exoskeleton and jointed legs
  • Two pairs of antennae
  • Compound eyes
  • Jointed limbs on each body segment, modified on head segments
• Insects


  • Segmented bodies with firm exoskeleton
  • Three pairs of jointed legs
  • Compound eyes
  • Two pairs of wings
  • Head, thorax and abdomen regions
  • Only one pair of antennae and three pairs of legs, no limbs on abdomen
• Arachnids


  • Body divided into cephalothorax and abdomen
  • Four pairs of limbs on cephalothorax
  • Pedipalps used in reproduction
  • Chelicerae used to pierce and paralyse prey
  • Several pairs of simple eyes
• Myriapods


  • Head and segmented body not obviously divided into thorax and abdomen
  • Pair of legs on each body segment, abdominal segments fused in pairs
  • One pair of antennae and simple eyes
• Vertebrates


  • Have a vertebral column
  • Poikilothermic (cold-blooded) or homoiothermic (warm-blooded)
• Fish


  • Poikilothermic (cold-blooded) vertebrates
  • Streamlined shape
  • Covered in overlapping scales
  • Have fins
  • Breathe through filamentous gills
  • Reproduce sexually with external fertilisation
• Homoiothermic


  Constant temperature
• Internal regulatory mechanisms keep the body temperature within narrow limits
• Fish


  • Poikilothermic (cold blooded) vertebrates
  • Smooth, streamlined shape
  • Covered with overlapping scales
  • Have fins
  • Breathe through filamentous gills
  • Reproduce sexually with external fertilisation
• Amphibia


  • Poikilothermic (cold blooded) vertebrates
  • Have four limbs and no scales
  • Spend part of life in water and part on land
  • Moist skin with capillaries to exchange gases
  • Have lungs but no diaphragm or ribs
  • Reproduce with external fertilisation
• Reptiles


  • Land-living vertebrates
  • Dry, scaly skin that resists water loss
  • Lay eggs with tough, parchment-like shells
  • Can regulate temperature to some extent by basking in the sun
• Birds


  • Homoiothermic (warm blooded) vertebrates
  • Flexible vertebral column in neck, rest fused for rigid structure
  • Covered in feathers of different types
  • Have four limbs, with forelimbs modified into wings
  • Have beaks
  • Reproduce with internal fertilisation and lay hard-shelled eggs
• Mammals


  • Homoiothermic (warm blooded) vertebrates
  • Have hair rather than feathers
  • Have a diaphragm for breathing
  • Have mammary glands to produce milk for young
  • Give birth to live young rather than laying eggs
  • Undergo internal fertilisation and development in the uterus
• Ferns are land plants with quite highly developed structures, including stems, leaves, roots, vascular tissue, and multicellular roots
• Ferns


  • Produce gametes but no seeds
  • Reproduce by producing single-celled spores from sporangia on the leaves
• Monocotyledons


  Flowering plants with only one cotyledon in their seeds, often with long, narrow leaves and parallel leaf veins
• Dicotyledons


  Flowering plants with two cotyledons in their seeds, often with broad leaves and branching leaf veins
• Most fungi are made up of thread-like hyphae rather than cells, and have many nuclei distributed throughout the cytoplasm
• Bacteria are single-celled organisms with a cell wall made of proteins, sugars and lipids, and a single circular chromosome not enclosed in a nuclear membrane
• Protoctists are single-celled organisms with their chromosomes enclosed in a nuclear membrane
• Some protoctists, like Euglena, have chloroplasts and can photosynthesize, while others, like Amoeba and Paramecium, take in and digest solid food
• Circular strand of DNA

  • Not enclosed in a nuclear membrane
  • Coiled up to occupy part of the cell
• Individual bacteria


  • May be spherical, rod-shaped or spiral
  • Some have filaments called flagella projecting from them
  • Flagella can flick and move the bacterial cell about