Study guide: Year 9 Cell Biology

📋 Course Outline

1. Eukaryotic Cell Structures
2. Prokaryotic Cell Features
3. Light and Electron Microscopes
4. Units and Microscope Magnification
5. Magnification Calculations
6. Specialised Cell Adaptations
7. Microscope Practical
8. Retrieval Foundations

📖 1. Eukaryotic Cell Structures

🔑 Key Concepts & Definitions

• Eukaryotic cell: has a nucleus containing DNA in large linear chromosomes; animal, plant, fungal and protist cells are eukaryotic
• Cytoplasm: a jelly-like material containing dissolved nutrients, salts and organelles where many chemical reactions occur
• Nucleus: contains genetic material, including DNA, and controls the activities of the cell

★ Must-know

• The cell membrane is permeable to some substances but not others and controls the movement of substances into and out of the cell.

• Mitochondria contain the enzymes for respiration and are where most energy is released during respiration.

Further detail

• Plant cells additionally contain chloroplasts, a cellulose cell wall and a permanent vacuole filled with cell sap.

💡 Memory Hook

Nucleus present in eukaryotes, absent in prokaryotes

📖 2. Prokaryotic Cell Features

🔑 Key Concepts & Definitions

• Plasmid: a small ring of DNA in a bacterial cell that can carry useful genes such as antibiotic resistance

★ Must-know

• Bacteria are prokaryotic cells that are 0.2 μm–2 μm long and do not have a nucleus.

• A bacterial chromosome is a single loop of DNA found freely in the cytoplasm.

Further detail

• Some bacteria have a flagellum, a strand of protein that acts like a propeller to move the cell forwards.

• Some bacteria have a slime capsule that protects them.

💡 Memory Hook

A tiny bacterial loop of DNA with plasmid rings and a flagellum

📖 3. Light and Electron Microscopes

🔑 Key Concepts & Definitions

• Resolution: the ability to distinguish between two objects as separate points

★ Must-know

📌 A light microscope uses a beam of light, can magnify up to ×2,000 and can be used to observe living specimens.

📌 An electron microscope uses a high-energy electron beam, can magnify up to ×2,000,000 and produces images with higher magnification and resolution.

Further detail

📌 Light microscopes are relatively cheap, easy to use, require little space and produce two-dimensional images, whereas electron microscopes are expensive, require special conditions and trained scientists, and can produce three-dimensional images.

💡 Memory Hook

Light microscopes can view living specimens, whereas electron microscopes provide greater resolution but require dead specimens

📖 4. Units and Microscope Magnification

★ Must-know

📐 Formula - Overall microscope magnification equals the eyepiece lens magnification multiplied by the objective lens magnification: $M = E \times O$.

• The units used for microscopic measurements include nanometres (nm), micrometres (μm) and millimetres (mm), and values must be converted into compatible units before calculation.

Further detail

• The eyepiece lens has a magnification of ×10 in the microscope examples.

💡 Memory Hook

Eyepiece × objective = overall magnification

📖 5. Magnification Calculations

★ Must-know

📐 Formula - Magnification is calculated using $M = \frac{I}{A}$, where image size is divided by actual size.

• 🔄 Magnification calculations require these steps:
  1. Measure image size in millimetres
  2. Convert image and actual sizes to the same unit
  3. Apply the appropriate formula

Further detail

📐 Formula - Image size is calculated using $I = A \times M$.

💡 Memory Hook

AIM: Actual size = Image size ÷ Magnification

📖 6. Specialised Cell Adaptations

🔑 Key Concepts & Definitions

• Differentiation: the process by which a cell changes to become specialised for a particular function

📝 Essential Points

• A nerve cell has many dendrites, a long axon and synapses that allow it to carry electrical impulses and pass them between cells.

• Muscle cells contain sliding fibres, many mitochondria and glycogen, allowing them to contract using energy from respiration.

• Sperm cells have a tail for movement, a mitochondria-rich middle section, digestive enzymes in the acrosome and a large nucleus containing half the genetic information needed to make a human.

• Root hair cells absorb water and minerals using a large surface area, a large permanent vacuole and many mitochondria for active transport.

• Palisade cells contain many chloroplasts with chlorophyll and are usually found in outer leaf and stem layers to absorb light for photosynthesis.

💡 Memory Hook

Cell structures adapt to their function, causing specialised cells to work efficiently

📖 7. Microscope Practical

★ Must-know

• The microscope practical involves placing a slide on the stage, selecting the lowest-power objective lens, focusing with the coarse and fine adjustment wheels, switching to a higher-power lens, refocusing with the fine adjustment wheel, and drawing and labelling the cells.

Further detail

📌 The magnification written below a microscope drawing is calculated by multiplying the objective magnification by the eyepiece magnification.

📌 Microscope drawings should be made clearly in pencil, labelled with visible cell structures and accompanied by the magnification used.

💡 Memory Hook

Stage, select, focus, switch, refocus, draw, label, calculate

📖 8. Retrieval Foundations

🔑 Key Concepts & Definitions

• Diffusion: the passive movement of particles from a high concentration to a low concentration
• Enzyme: An enzyme is a biological catalyst that speeds up chemical reactions.

★ Must-know

• Aerobic respiration is a chemical reaction that releases energy and occurs with oxygen.

Further detail

• Photosynthesis is a chemical reaction that requires energy from the Sun.

• The digestive system includes organs that release enzymes, mechanically break down food, absorb nutrients and absorb water, while food passes directly through the oesophagus, stomach, small intestine, large intestine and rectum.

📊 Synthesis Tables

Light and Electron Microscopes

Feature	Light microscope	Electron microscope
Radiation	Beam of light	High-energy electron beam
Maximum magnification	×2,000	×2,000,000
Specimen	Can be living	Must be dead
Image	Two-dimensional	Three-dimensional possible