Cell Structure And Size Of Specimens

Animal Cell Structure

• Animal cells have a cell membrane, cytoplasm, nucleus, mitochondria and ribosomes.
• The cell membrane controls what enters and leaves the cell.
• The nucleus contains the genetic material (DNA).
• Mitochondria are the site of aerobic respiration.

Which structure is found in animal cells?

• Cell wall
• Chloroplast
• Mitochondrion
• Permanent vacuole

Plant Cell Structure

• Plant cells have all the features of animal cells plus a cellulose cell wall, chloroplasts and a permanent vacuole.
• The cell wall provides structural support and gives a rigid shape.
• Chloroplasts contain chlorophyll and absorb light for photosynthesis.
• The permanent vacuole stores cell sap and helps support the cell.

Which of these are true?

• Plant cells have a cell wall made of cellulose.
• Animal cells contain chloroplasts.
• Both animal and plant cells have mitochondria.
• Plant cells have a permanent vacuole.

Bacterial Cell Structure

• Bacteria are single-celled organisms with a different structure to animal and plant cells.
• They have a cell wall made of peptidoglycan (not cellulose).
• They contain circular DNA and may have plasmids (small loops of DNA).
• Bacteria lack a nucleus, mitochondria and chloroplasts.

Bacterial cells have a cell wall made of ____ and contain ____ DNA.

Functions of Cell Structures

• Nucleus: contains genetic material (DNA).
• Mitochondria: site of aerobic respiration.
• Ribosomes: site of protein synthesis.
• Cell membrane: controls passage of substances in and out.
• Chloroplasts (plants): absorb light for photosynthesis.
• Cell wall (plants/bacteria): provides structural support.

What is the function of ribosomes?

• Aerobic respiration
• Protein synthesis
• Photosynthesis
• Storage of cell sap

Organisation of Cells

• Cells are the basic unit of life.
• Similar cells work together to form tissues.
• Different tissues work together to form organs.
• Organs work together in organ systems.
• Example: palisade mesophyll cells → leaf tissue → leaf (organ) → shoot system.

Which of these are correct levels of organisation?

• Cell → tissue → organ → organ system
• Organ → cell → tissue → organ system
• Tissue → organ → cell → organ system
• Cell → organ → tissue → organ system

Magnification Formula

• Magnification = image size ÷ actual size.
• Use the formula triangle: $M = I / A, I = M \times A, A = I / M$.
• Units must be the same (e.g. both in mm).
• Magnification has no units (e.g. $\times 100)$.

If an image is 30 mm and the actual size is 0.01 mm, the magnification is ____.

Converting Between Units

• 1 $mm = 1000$ μm (micrometres).
• To convert mm to μm, multiply by 1000.
• To convert μm to mm, divide by 1000.
• Always check units before using the magnification formula.

How many micrometres (μm) are in 1 mm?

• 10
• 100
• 1000
• 0.001

Size of Specimens

• Cells are typically measured in micrometres (μm).
• Animal cells: 10–30 μm; plant cells: 10–100 μm.
• Bacteria: 1–5 μm.
• Use the magnification formula to calculate actual size from magnified images.

A cell measures 50 μm. In mm this is ____ mm.

A plant cell is 0.1 mm long. What is its length in μm?

• 1
• 10
• 100
• 1000

Summary

• Animal cells: membrane, cytoplasm, nucleus, mitochondria, ribosomes.
• Plant cells also have: cell wall, chloroplasts, permanent vacuole.
• Bacteria: cell wall (peptidoglycan), circular DNA, plasmids, no nucleus.
• Organisation: cells → tissues → organs → organ systems.
• Magnification: $M = I /$ A; convert units (1 $mm = 1000$ μm).