Study guide: Cell Biology and Transport

📋 Course Outline

1. Eukaryotic and Prokaryotic Cells
2. Cell Structures and Their Functions
3. Specialised Cells and Adaptations
4. Light and Electron Microscopes
5. Magnification and Image Size
6. Diffusion and Osmosis
7. Active Transport and Examples

📖 1. Eukaryotic and Prokaryotic Cells

📝 Essential Points

📌 Animal and plant cells are eukaryotic, with DNA organised into chromosomes inside a nucleus, whereas bacteria are prokaryotic and lack a nucleus.

• Bacteria are single-celled, smaller than eukaryotic cells, and contain a single loop of DNA plus small DNA rings called plasmids.

💡 Memory Hook

Eukaryotes keep DNA in a nucleus; prokaryotes have a DNA loop without one.

📖 2. Cell Structures and Their Functions

★ Must-know

• The cell membrane controls the movement of substances into and out of a cell.

• The nucleus contains DNA, mitochondria release energy through respiration, and ribosomes are the site of protein synthesis.

• Plant cell structures have these functions:

  • The cellulose cell wall strengthens the cell
  • The permanent vacuole contains cell sap
  • Chloroplasts contain chlorophyll to absorb light energy for photosynthesis

Further detail

• The cytoplasm is a jelly-like substance where chemical reactions happen.

📖 3. Specialised Cells and Adaptations

★ Must-know

📌 Most animal cells differentiate early in development, whereas plant cells differentiate throughout the plant's lifetime.

• A sperm cell fertilises an ovum and is adapted with a tail for swimming and many mitochondria to release energy for swimming.

• A red blood cell transports oxygen and has no nucleus, contains haemoglobin that binds oxygen, and has a flat biconcave disc shape that increases its surface-area-to-volume ratio.

• A muscle cell contracts and relaxes to allow movement and contains contractile protein fibres and many mitochondria that release energy for contraction.

• A nerve cell carries electrical impulses and has branched dendrites for connections with other neurones or effectors and a myelin sheath that insulates the axon and increases impulse transmission speed.

• A root hair cell absorbs water and mineral ions from soil; its long projection increases surface area, and many mitochondria supply energy for mineral-ion active transport.

Further detail

• A palisade cell carries out photosynthesis and has many chloroplasts containing chlorophyll and is located near the top surface of the leaf to absorb the most light.

📖 4. Light and Electron Microscopes

★ Must-know

📌 A light microscope uses light and can view living samples, whereas an electron microscope uses a beam of electrons and cannot view living samples.

Further detail

📌 Electron microscopes are more expensive and have higher magnification and resolution than light microscopes.

• Electron microscopes can reveal sub-cellular structures such as ribosomes that are too small to be seen with a light microscope.

💡 Memory Hook

Light shows living samples; electron gives higher magnification and resolution but cannot show living samples.

📖 5. Magnification and Image Size

📝 Essential Points

📐 Formula - Magnification equals image size divided by actual size: $\text{magnification}=\frac{\text{image size}}{\text{actual size}}$.

📖 6. Diffusion and Osmosis

🔑 Key Concepts & Definitions

• Diffusion: The net movement of particles from an area of higher concentration to an area of lower concentration, down a concentration gradient, without energy from respiration.
• Osmosis: The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

📝 Essential Points

• The rate of diffusion is affected by:

  • The concentration difference
  • Temperature
  • Membrane surface area

• In humans, nutrients diffuse from the small intestine into capillaries through villi, oxygen diffuses from alveolar air into capillary blood, carbon dioxide diffuses from capillary blood into alveolar air, and urea diffuses from cells into the blood for excretion in the kidney.

• In fish, oxygen diffuses from water passing over the gills into blood in the gill filaments, while carbon dioxide diffuses from the blood into the water.

• In plants, carbon dioxide used for photosynthesis diffuses into leaves through stomata, and oxygen produced during photosynthesis diffuses out through the stomata.

💡 Memory Hook

Diffusion moves particles down a gradient; osmosis moves water across a partially permeable membrane.

📖 7. Active Transport and Examples

🔑 Key Concepts & Definitions

• Active transport: The movement of particles against a concentration gradient, from a lower concentration to a higher concentration, using energy released by respiration.

★ Must-know

📌 Diffusion and osmosis are passive processes that do not require energy, whereas active transport requires energy released by respiration.

Further detail

• In plants, water moves by osmosis from dilute soil solution into the more concentrated root hair cell.

• In plants, active transport absorbs mineral ions into root hair cells from more dilute soil solutions, against the concentration gradient.

• In the small intestine, active transport allows sugar molecules to be absorbed into the blood when sugar concentration is lower in the intestine than in the blood.

💡 Memory Hook

Passive transport follows the gradient; active transport moves against it using respiratory energy.