01 · Explore
Groups of cells share different jobs
Connect cells, tissues, organs and systems.
- Tissue
- Cells organised to work together in a related function; a complex tissue can contain different cell types.
- Division of labour
- Different parts carry out different jobs that support the whole organism.
Muscle tissue contracts; nervous tissue carries signals. A leaf contains protective, photosynthetic and conducting tissues working together.
Cells form tissues; several tissues form an organ; organs cooperate in systems. A single-celled organism instead carries out its life activities within one cell.
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Question
Must every cell in a tissue look identical?
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02 · Explore
Structure fits the way an organism lives
Compare growth, support, movement and nutrition.
- Specialisation
- A structure adapted to perform a particular job.
A plant’s cell walls and supporting tissues help it stand upright. Photosynthetic tissues make food, and conducting tissues move water and food.
Animals have flexible tissues for movement, tissues for processing food, and transport and coordination systems. Some animals are fixed in one place, so “all animals move around” is not a safe rule.
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Question
Why does one general tissue not do every job equally well?
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03 · Explore
Growth begins with dividing cells
Then new cells develop specialised structures.
- Meristematic tissue
- Plant tissue with actively dividing cells.
- Differentiation
- Development of specialised structure and function.
Division adds cells; differentiation gives them jobs
- Model
- An illustrative cell pathway. A daughter cell may stay meristematic or differentiate; the drawing does not imply only two mature cell types.
Meristem cells are closely packed, with thin walls, dense cytoplasm and a prominent nucleus. Large mature vacuoles are usually absent; they are suited to active division.
Some daughter cells remain dividing; others become permanent tissues. “Permanent” does not mean every such cell is dead: many remain alive and perform specialised functions.
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Question
Can a permanent plant tissue be alive?
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04 · Explore
Locate the three growth zones
Match each position to its effect.
- Apical meristem
- At root and shoot tips; helps increase length.
- Lateral meristem
- Along sides of relevant stems and roots; helps increase girth.
- Intercalary meristem
- Growth region at leaf or internode bases, especially in grasses.
Growth zones are in different places
- Model
- Schematic plant. Orange marks growing tips; violet marks a girth-growth zone. The blue basal growth band represents an intercalary meristem in a grass, not every dicot stem.
Removing a root tip removes its main apical growth zone. Cambium can add cells inward and outward, increasing stem thickness. Growth rings can record seasonal growth, but ring counting needs care.
Grass can regrow from basal intercalary regions after mowing. New branches after pruning involve buds; do not attribute all branching to intercalary meristems.
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Question
Which growth zone increases a woody stem’s girth?
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05 · Explore
The outside layer protects and exchanges
The barrier also has specialised openings.
- Epidermis
- The outer cell covering of the plant.
- Cuticle
- A waxy covering that helps reduce water loss.
- Stoma
- An epidermal pore regulated by guard cells.
A pore interrupts the protective surface
- Model
- Schematic stoma viewed from above. Two guard cells border a pore. The arrows show exchange pathways, not a measured flow rate.
- Pore
- The narrow space between the two orange guard cells is the opening; it is not a third cell.
Closely packed epidermal cells protect inner tissues. Root hairs increase absorption surface; leaf stomata allow gas exchange and water-vapour loss.
A thick cuticle can reduce water loss in dry habitats. Older stems can develop cork: tightly packed dead cells with water-resistant walls. A leaf’s cuticle is not the same as its stomatal opening.
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Question
Why can fewer stomatal openings reduce water loss but also limit photosynthesis?
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06 · Explore
Thin walls, flexible corners, strong walls
Match the cell wall to the support needed.
- Parenchyma
- Living, usually thin-walled cells; storage and other functions.
- Collenchyma
- Living cells with unevenly thickened walls, often at corners; flexible support.
- Sclerenchyma
- Cells with thick lignified walls; commonly dead at functional maturity.
Parenchyma can store material, contain chloroplasts or form air-space tissue in aquatic plants. Collenchyma supports young flexible parts.
Sclerenchyma gives stiffness and strength, for example in many fibres and hard seed coverings. Living parenchyma does not provide the same thick lignified support.
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Question
Which tissue is suited to a young stalk that bends without snapping?
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07 · Explore
A water pathway can use hollow dead cells
Follow water and minerals from roots towards shoots.
- Xylem
- Complex tissue conducting water and mineral ions and providing support.
Vessels and tracheids become hollow conducting elements with strengthened walls. Xylem fibres support; xylem parenchyma remains living and supports storage and other functions.
Transpiration from leaves helps pull a continuous water column upward. The conducting walls do not need to be living pumps. Not every xylem cell is dead.
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Question
Why is an empty strengthened lumen useful in a water-conducting element?
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08 · Explore
Food moves from sources to places that use it
Different living cells cooperate in transport.
- Phloem
- Complex tissue transporting dissolved food materials, especially sugars.
- Sieve tube / companion cell
- Conducting sieve-tube cells work with nearby living companion cells.
Sieve plates connect long sieve-tube elements. Companion cells support their functioning and loading and unloading; parenchyma stores materials, and fibres support.
Transport connects a source, such as a leaf, with a sink, such as a growing root or fruit. It can proceed upwards or downwards in different tubes, depending on the source and sink.
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Question
Must phloem transport always move down the stem?
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