Life Science: Cells, Body Systems, and Reproduction
What you must understand
All living things are made of cells, the basic unit of structure and function. Know the shared structures - cell membrane, cytoplasm, nucleus, mitochondria, ribosomes - and the differences between plant and animal cells: plant cells have a cell wall, chloroplasts, and a large central vacuole. Understand diffusion (movement from high to low concentration) and osmosis (diffusion of water across a membrane), and why cells must exchange materials with their environment.
At the organism level, know that cells form tissues, tissues form organs, organs form organ systems. Be able to connect major systems to their functions: digestive (break down and absorb nutrients), circulatory (transport materials), respiratory (gas exchange), nervous (detect and respond), muscular and skeletal (support and movement), and excretory (remove wastes).
For reproduction, distinguish asexual reproduction (one parent, offspring genetically identical, e.g., budding, binary fission) from sexual reproduction (two parents, offspring genetically varied). Know that mitosis produces body cells with the same chromosome number, while meiosis produces sex cells with half the chromosome number, restoring the full number at fertilization.
Traps to expect
Questions often confuse mitosis with meiosis, or claim offspring from asexual reproduction are genetically varied. Watch for statements implying that a single body system works alone - systems are interdependent. Another trap is treating the cell wall as a membrane that controls what enters.
Worked example / rule of thumb
If a cell is placed in pure water and swells, water moved into the cell by osmosis, from higher water concentration outside to lower inside. Rule of thumb: water follows concentration gradients, and structure matches function.
Key ideas
- Cell structures and plant vs. animal differences
- Diffusion and osmosis
- Levels of organization from cell to organ system
- Major body systems and their roles
- Mitosis vs. meiosis; asexual vs. sexual reproduction