IGCSE biology Revision

• Viruses are not considered living organisms as they do not meet all seven requirements of living organisms
• Animals:

  • Multicellular organisms
  • Heterotrophs
  • Most reproduce sexually
• Plants:

  • Multicellular organisms
  • Autotrophs
  • Obtain energy from the sun through photosynthesis
  • Around 300,000 species
• Fungi:

  • Some are multicellular, some are unicellular
  • Heterotrophs
  • Obtain energy from other organisms
  • Most fungi feed using saprotrophic nutrition
  • Some fungi can be pathogens
  • Multi-solar fungi have a body called a mycelium made up of hyphae
• Protists:

  • Unicellular organisms
  • Some have chloroplasts for photosynthesis
  • Some consume other organisms for energy
  • Some can be pathogens
• Bacteria:

  • Single-celled organisms
  • Live in various environments
  • Most feed off other organisms
  • More species of bacteria than all other kingdoms combined
  • Some bacteria can cause disease, but many are helpful
• Viruses:

  • Super tiny particles
  • Not living organisms
  • Reproduce inside living cells
  • Depend on other organisms to grow and reproduce
  • Considered pathogens as they cause harm to other living organisms
  • Examples include influenza virus, tobacco mosaic virus, HIV, and COVID-19
• Organelles, also known as subcellular structures, are the parts that make up a cell like the nucleus, ribosomes, and mitochondria
• Each individual organelle has a specific role to play
• Multiple organelles together form a single cell
• Cells come in various shapes and sizes and contain different combinations and numbers of organelles
• Specialized cells include epithelial cells, muscle cells, and different types of glandular cells
• Tissues are groups of similar cells that work together to carry out a specific function
• Examples of tissues include epithelial tissue, muscle tissue, and glandular tissue
• Organs are groups of different tissues that work together to perform a particular function
• For example, epithelial tissue, muscular tissue, and glandular tissue may work together to form an organ like the stomach
• Organ systems are groups of organs that work together to perform a specific function
• Examples of organ systems include the digestive system, cardiovascular system, and reproductive system
• The whole organism is the highest level, with multiple organ systems working together to form the organism
• There are about 12 different organ systems, including the immune system, nervous system, respiratory system, endocrine system, and urinary system
• Cells are the basic building blocks of life and the smallest unit of life that can replicate independently
• Animal and plant cells are examples of eukaryotic cells
• Bacterial cells are prokaryotic cells
• Animal and plant cells are multicellular, containing many cells
• Bacterial cells are unicellular, consisting of a single cell
• Animal and plant cells have cell membranes that control substances passing in and out
• Both types of cells have a nucleus containing genetic material (DNA) that controls cell activities
• Both types of cells are filled with cytoplasm, where chemical reactions take place
• Both animal and plant cells have mitochondria that provide energy for cell function through aerobic respiration
• Both animal and plant cells contain ribosomes, the site of protein synthesis
• Plant cells have a rigid cell wall made of cellulose for support and structure
• Plant cells have a permanent vacuole containing cell sap for storage
• Plant cells have chloroplasts where photosynthesis occurs, containing chlorophyll
• Bacterial cells have a cell membrane, cell wall, ribosomes, and cytoplasm
• Bacterial cells have a single circular strand of DNA called the nucleoid, instead of a nucleus
• Some bacteria have plasmids, small rings of DNA carrying extra genes like antibiotic resistance
• Some bacteria have flagella, thread-like structures that allow movement
• Biological molecules are the building blocks to make cells and other key structures required for living organisms
• As a human, you get these molecules through your diet by eating
• The most important three types of biological molecules are carbohydrates, lipids, and proteins