Cell Biology: Quick Revision Notes

Biological Cells

• Cells are the smallest units of life; basic building blocks of all living things; extremely small and visible only with a microscope.

Living and Non-Living

• Living things are characterized by 7 features (MRS Gren): Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition.
• Use an acronym or memory aid to recall these seven features.

The 7 Characteristics of Living Things (MRS Gren)

• Movement: ability to move or change position (even plants move, e.g., leaves towards light).
• Respiration: energy from nutrients converted to usable form (often glucose breakdown).
• Sensitivity: detect and respond to environment (nerve signals; plant responses to light/gravity).
• Growth: irreversible increase in size/mass via cell division and expansion.
• Reproduction: produce offspring to continue the species.
• Excretion: removal of waste to maintain internal balance.
• Nutrition: intake and use of nutrients for energy and growth.

Cell Theory

• The cell is the smallest unit that sustains life.
• All living things are made up of cells.
• All cells come from pre-existing cells.

Unicellular vs Multicellular

• Unicellular: organisms made of a single cell (e.g., Amoeba).
• Multicellular: organisms made of many cells (humans, plants).

Levels of Organisation

• Cell → Tissue → Organ → Organ System → Organism.
• The cell is the smallest unit; similar cells form tissues; tissues form organs; organs form organ systems; organ systems make up the organism.

Tissues and Organs

• Tissues are groups of similar cells performing a common function.
• Organs are structures made of multiple tissues working together.
• Examples include muscle tissue, epithelium, etc.

Plant vs Animal Cells (Key Differences)

• Plant cells contain chloroplasts for photosynthesis and a large central vacuole; have a rigid cell wall.
• Animal cells do not have chloroplasts or a cell wall and usually have smaller vacuoles.
• Both contain mitochondria and ribosomes; both perform energy production and protein synthesis.

The Microscope

• A microscope is used to magnify small objects for viewing.
• Parts include: ocular lens, objective lenses, stage, light source, coarse and fine focus, diaphragm, arm, base.
• Magnification increases as you switch to higher-power objective lenses; field of view decreases with higher magnification.
• Field of View: what you can see through the eyepiece; higher magnification = see more detail but less of the specimen.

Calculating Total Magnification

• Formula: $\text{Total magnification} = \text{Objective} \times \text{Ocular}$
• Example: $4\times \text{ objective} \times 10\times \text{ ocular} = 40\times$ total magnification.

Using a Microscope Practically

• Goals include describing specimen orientation under different magnifications and drawing/ describing everyday objects as seen through the microscope.
• If you can't find your specimen under high-power lenses, check alignment and focusing procedures.

Observing Plant and Animal Cells

• Organelles not living on their own; together form living cells.
• Common organelles include nucleus (brain), mitochondria (energy), chloroplasts (photosynthesis in plants), Golgi bodies (packaging/shipping), endoplasmic reticulum (transport), ribosomes (protein synthesis), cytoplasm, vacuoles, cell membrane, cell wall (plants).
• Practice observing plant and animal cells under a microscope and noting similarities/differences.

Specialised Cells

• Specialized cells are adapted for specific functions (e.g., red blood cells, nerve cells, muscle cells, sperm cells, ovum, bone cells).
• Multicellular organisms have cells that differentiate to perform particular roles.

Organelle overview (quick reference)

• Nucleus: brain of the cell; stores genetic material.
• Cell membrane: gatekeeper, controls what enters/leaves.
• Cytoplasm: jelly-like interior where organelles reside.
• Mitochondria: powerhouses, energy production.
• Chloroplasts: photosynthesis in plants.
• Golgi apparatus: processes and packages materials.
• Endoplasmic reticulum (rough and smooth): transport and synthesis.
• Ribosomes: protein synthesis.
• Vacuole: storage (larger in plant cells).
• Cell wall: rigid support in plant cells.

Scale and Measurement (Units)

• Scale of the universe and measurement units cover milli-, micro-, nano- etc.
• Prefix ladder (examples):
  • kilo, hecto, deca (10^3, 10^2, 10^1)
  • base unit (10^0)
  • deci, centi, milli (10^-1, 10^-2, 10^-3)
  • micro (10^-6)
• Conversions (examples from the slides):
  • 5.23 m to nm: $5.23~\text{m} \times 10^{9} = 5.23 \times 10^{9}~\text{nm}$
  • 6.72 μm to cm: $6.72~\mu\text{m} \div 10^{4} = 6.72 \times 10^{-4}~\text{cm}$
  • 8.46 km to cm: $8.46~\text{km} = 8.46 \times 10^{5}~\text{cm}$

Quick Look at Observed Objects under Microscope

• Leaf, silk, human hair, bone tissue, banana peel were used as examples of what you can observe.

Revision Prompts (Recall)

• Where do all cells come from? (Cell Theory: from pre-existing cells.)
• What levels of organisation follow cell → tissue → organ → organ system → organism?
• What are the seven characteristics of living things (MRS Gren) with examples?
• How do plant and animal cells differ in organelles and structure?

End of Notes