7th Grade Science: Cells

• Chapter 4 of a 7th-grade general science curriculum typically covers a variety of scientific topics suitable for that age group.

Cells: The Basic Units of Life

• Cells are the fundamental building blocks of all living organisms.
• Some organisms are unicellular (made of only one cell), while others are multicellular (made of many cells).
• The cell theory states that all living things are composed of cells, cells are the basic units of structure and function in living things, and new cells are produced from existing cells.
• Key cell structures include the cell membrane, cytoplasm, nucleus, and organelles.
• The cell membrane controls what enters and exits the cell.
• The cytoplasm is the gel-like substance inside the cell where organelles are located.
• The nucleus contains the cell's genetic material (DNA) and controls the cell's activities.
• Organelles are specialized structures within the cell that perform specific functions.
  • Examples: mitochondria (energy production), ribosomes (protein synthesis), endoplasmic reticulum (protein and lipid synthesis), Golgi apparatus (processing and packaging), lysosomes (waste disposal), vacuoles (storage).
• Plant cells have additional structures like a cell wall (provides support and shape) and chloroplasts (site of photosynthesis).
• Cells can be specialized to perform specific functions in multicellular organisms (e.g., nerve cells, muscle cells, blood cells).

Classification of Living Things

• Taxonomy is the science of classifying and naming organisms.
• Organisms are grouped based on shared characteristics.
• The Linnaean system of classification uses a hierarchical system.
• The main levels of classification are: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.
• The three domains of life are: Bacteria, Archaea, and Eukarya.
• Kingdoms within Eukarya include: Protista, Fungi, Plantae, and Animalia.
• Scientific names are written in binomial nomenclature (Genus species) and are usually italicized or underlined.

Plants and Photosynthesis

• Plants are autotrophs, meaning they produce their own food through photosynthesis.
• Photosynthesis is the process by which plants convert light energy, water, and carbon dioxide into glucose (sugar) and oxygen.
• Chlorophyll, a green pigment found in chloroplasts, absorbs light energy.
• The equation for photosynthesis: 6CO2 + 6H2O + Light Energy -> C6H12O6 + 6O2.
• Plants have vascular tissues (xylem and phloem) to transport water and nutrients.
• Xylem transports water and minerals from the roots to the rest of the plant.
• Phloem transports glucose from the leaves to other parts of the plant.
• Plant structures include roots, stems, leaves, and flowers.
• Roots anchor the plant and absorb water and nutrients.
• Stems provide support and transport substances.
• Leaves are the primary sites of photosynthesis.
• Flowers are involved in reproduction.

Animals and Their Adaptations

• Animals are heterotrophs, meaning they obtain food by consuming other organisms.
• Animals are multicellular and have specialized tissues and organs.
• Animals can be classified into different groups based on their characteristics (e.g., vertebrates and invertebrates).
• Vertebrates have a backbone, while invertebrates do not.
• Adaptations are characteristics that help animals survive and reproduce in their environment.
• Adaptations can be physical (e.g., camouflage, sharp claws) or behavioral (e.g., migration, hibernation).
• Examples of animal adaptations:
  • Camouflage helps animals blend in with their surroundings.
  • Mimicry allows one animal to resemble another for protection.
  • Migration is the seasonal movement of animals from one region to another.
  • Hibernation is a state of inactivity that allows animals to conserve energy during the winter.

Ecosystems and Interactions

• An ecosystem is a community of living organisms interacting with each other and their physical environment.
• Ecosystems include biotic factors (living organisms) and abiotic factors (non-living components like water, sunlight, and temperature).
• Organisms in an ecosystem can be classified as producers, consumers, or decomposers.
• Producers (autotrophs) produce their own food (e.g., plants).
• Consumers (heterotrophs) obtain food by eating other organisms (e.g., herbivores, carnivores, omnivores).
• Decomposers break down dead organisms and waste, returning nutrients to the ecosystem (e.g., bacteria, fungi).
• Food chains and food webs show the flow of energy through an ecosystem.
• A food chain is a linear sequence of organisms where each organism feeds on the one before it.
• A food web is a more complex network of interconnected food chains.
• Energy pyramids show the amount of energy available at each trophic level in an ecosystem.
• Energy decreases as it moves up the trophic levels.
• Relationships between organisms in an ecosystem include:
  • Predation (one organism hunts and kills another).
  • Competition (organisms compete for resources).
  • Symbiosis (close interaction between two different species).
    • Mutualism (both species benefit).
    • Commensalism (one species benefits, and the other is not harmed).
    • Parasitism (one species benefits, and the other is harmed).