Grade 8 Science: Cells and Body Systems

• These Grade 8 science notes cover Cells and Body Systems.
• The unit explores cell theory, cell structure, levels of organization, and various body systems.

Cell Theory and Cell Structure

• Cell theory has three main components: all living things are made of cells, the cell is the basic unit of life, and all cells come from pre-existing cells.
• Cells must maintain a high surface area to volume ratio to efficiently exchange materials with their environment.

Cell Organelles and Their Functions

• Cell Membrane: controls the movement of substances in and out.
• Nucleus: contains DNA and controls cell activities.
• Cytoplasm: is a gel-like substance where processes occur.
• Cytosol: is the fluid portion of the cytoplasm.
• DNA: is genetic material with instructions for cell functions.
• Mitochondria: produces energy through cellular respiration.
• Ribosomes: synthesizes proteins.
• Chloroplasts: (in plant cells only) are the site of photosynthesis.
• Vesicles: are small sacs that transport materials.

Plant vs. Animal Cells

• Plant cells have a cell wall, chloroplasts, and a large central vacuole.
• Animal cells lack a cell wall and chloroplasts, but have centrioles.

Unicellular vs. Multicellular Organisms

• Unicellular organisms consist of a single cell performing all life functions.
• Examples of unicellular organisms: bacteria, amoeba
• Multicellular organisms have specialized cells that work together.
• Examples of multicellular organisms: humans, plants

Microscopes

• Electron microscopes provide high magnification and resolution.
• Compound light microscopes use multiple lenses to magnify small objects.
• Stereo light microscopes provide a 3D view of specimens.

Levels of Organization in the Body

• Cells are the basic unit of life.
• Tissues are groups of similar cells performing a function.
• Organs are structures made of tissues performing specific tasks.
• Body systems are groups of organs working together.

Digestive System

• Digestion is the breakdown of food into absorbable nutrients.
• Peristalsis are wave-like muscle contractions that move food.
• Chyme is a semi-liquid mass of food in the stomach.
• Villi are small finger-like projections in the intestines that absorb nutrients.
• Main organs of the digestive system: mouth, esophagus, stomach, small intestine, large intestine, liver, pancreas.
• Physical digestion involves breaking food into smaller pieces, for example, chewing.
• Chemical digestion involves breaking down food molecules using enzymes, for example, saliva breaking down starch.

Respiratory System

• Trachea: windpipe that directs air to the lungs.
• Bronchi: branches leading to each lung.
• Lungs: organs for gas exchange.
• Pharynx: passageway for air and food.
• Epiglottis: prevents food from entering the airway.
• Alveoli: tiny air sacs for oxygen and carbon dioxide exchange.
• Diaphragm: muscle that helps with breathing.

Circulatory System

• Heart: pumps blood.
• Capillaries: smallest blood vessels where gas exchange occurs.
• Veins: carry blood back to the heart.

Components of Blood

• Red blood cells: carry oxygen.
• Plasma: liquid portion transporting nutrients.
• White blood cells: fight infections.
• Platelets: help in blood clotting.

Heart Rate

• Heart rate measures how many times the heart beats per minute.
• Indicates fitness levels and overall health.
• More fit individuals tend to have lower resting heart rates.

Grade 8 science notes covering cells and body systems. The unit explores cell theory, cell structure, levels of organization, and body systems. Key topics include cell organelles, their functions, and the importance of surface area to volume ratio in cells.