Levels of organisation and why plant and animal tissues differ
A school has a principal, teachers, clerks and cleaners, and each group does its own job so the school runs smoothly. A many-celled body works the same way: groups of cells share the work.
A tissue is a group of similar cells that work together to do one job. Tissues join to form organs, and organs form organ systems. Plants and animals have different tissues because they live differently: plants stay in one place and make their own food, while most animals move about and digest food.
In the figure : Many-celled bodies are built level by level from cells.
Rule 1: Division of labour makes the body efficient — Different tissues do different jobs, so the whole body works better than if every cell did everything.
- Easy : Muscle tissue moves the body, nervous tissue controls it, and bone supports it.
- Medium : In an amoeba a single cell does every job, but in a human the work is shared among many tissues.
- Exam-type : The heart is an organ because it is made of more than one kind of tissue working together.
Rule 2: The lifestyle decides the tissues — Plants are fixed, need support and make food using sunlight, so their tissues suit support and photosynthesis. Most animals move and digest food, so their tissues suit movement, control and digestion.
- Easy : Plants have tough cell walls, which help them stand upright in one place.
- Medium : Animal cells have no cell wall, so they are flexible and help in movement.
- Exam-type : Xylem and phloem are plant tissues, while muscle and nervous tissue are animal tissues.
Tissue → organ → organ system → organism. Ask: how does this job suit the way the organism lives?
Thinking that a tissue always has only one kind of cell. Complex tissues such as xylem have more than one kind.
Memory clue: C-T-O-S-B — Cell, Tissue, Organ, System, Body. Plants stay and make food; animals move and digest.
Spot the difference
| Point | Plants | Animals |
|---|---|---|
| Movement | Mostly fixed in place | Most can move |
| Food | Make it by photosynthesis | Digest food they eat |
| Cell wall | Present (strong support) | Absent (flexible cells) |
Practice questions
- 1What is a tissue?
- 2Write the order of organisation from a cell to an organism.
- 3Name one tissue that carries water in plants.
- 4Why do plants need tough supporting tissues but animals need muscle tissue?
- 5How does division of labour help a many-celled body?
- 6Why is the heart called an organ and not a tissue?
- 7A body has bone, muscle and nerve cells. Which tissue controls the others and which one moves the body?
- 8An amoeba and a human both stay alive. How is the way each organises its work different?
Show answers (try them yourself first)
- 1A group of similar cells doing one job.
- 2Cell → tissue → organ → organ system → organism.
- 3Xylem.
- 4Plants are fixed and need strength to stand; animals move and muscles contract to produce movement.
- 5Each tissue does one job well, so the body is more efficient.
- 6Because it is made of several kinds of tissue working together.
- 7Nervous tissue controls; muscle tissue moves the body.
- 8An amoeba does every job with one cell; a human shares the jobs among many tissues.
Meristematic tissues and growth in plants
When you trim the top of a hedge, it grows bushier in a few weeks, and grass in a lawn grows back after mowing. This growth comes from special cells that keep dividing.
Meristematic tissue is made of actively dividing cells and is found only in growing regions of plants. Apical meristem lies at root and shoot tips and adds length. Lateral meristem lies along the sides of stems and roots and adds girth. Intercalary meristem lies at the base of nodes or leaves and helps regrowth.
In the figure : Each meristem adds growth in a different direction.
Rule 1: Match the meristem to the direction of growth — Tips → length, sides → thickness, base of node → regrowth after cutting.
- Easy : Root tips and shoot tips grow longer because of apical meristem.
- Medium : The trunk of a tree becomes thicker year by year because of lateral meristem.
- Exam-type : Grass grows back after cutting because intercalary meristem is at the base of its leaves.
Rule 2: Meristem cells are built for fast division — They have thin walls, dense cytoplasm, a large nucleus and little or no vacuole, and they sit closely packed. Later they differentiate into permanent tissue.
- Easy : A cell that becomes specialised for storage is no longer dividing; it has become a permanent tissue.
- Medium : Annual rings in a tree trunk: one ring per year, so counting them gives the tree's age.
- Exam-type : A teak trunk with 25 rings is about 25 years old; wide rings mean good growing years.
Apical = length, lateral = girth, intercalary = regrowth. Count the rings to find the age.
Saying meristem is found everywhere in a plant. It is only in the growing regions, such as tips, sides and the base of nodes.
Memory clue: A-L-I — Apical = tip = length, Lateral = side = girth, Intercalary = in between = regrowth.
Spot the difference
| Meristem | Where it is | Adds |
|---|---|---|
| Apical | Root and shoot tips | Length |
| Lateral | Sides of stem and root | Girth (thickness) |
| Intercalary | Base of nodes or leaves | Regrowth after cutting |
Practice questions
- 1What is meristematic tissue?
- 2Where is apical meristem found?
- 3What do annual rings in a tree trunk show?
- 4Why does cut grass grow back?
- 5How is a meristem cell different from a permanent cell?
- 6A teak tree has 30 rings. Estimate its age.
- 7A teak trunk was 24 cm wide at 20 years and 40 cm wide at 40 years. Find the average increase in width per year.
- 8Two onion roots are kept in water; the tips of one are cut off. Which keeps growing in length and why?
Show answers (try them yourself first)
- 1Tissue made of actively dividing cells in plants.
- 2At the tips of roots and shoots.
- 3The age of the tree, with one ring for each year.
- 4Intercalary meristem at the base of its leaves keeps dividing.
- 5A meristem cell has thin walls, dense cytoplasm and a large nucleus and divides; a permanent cell is specialised and has lost the ability to divide.
- 6About 30 years.
- 7(40 − 24) cm ÷ 20 years = 0.8 cm per year.
- 8The uncut root, because growth in length happens at the tip from apical meristem.
Protective tissue: epidermis and cuticle
A raincoat keeps rain off you, and a thin coat of wax keeps a polished fruit shiny and prevents it drying out. Plants also have an outer cover that protects them.
Epidermis is the outermost layer of the plant body, usually one layer of tightly packed cells. Its outer surface may carry a waxy cuticle made of cutin. It has pores called stomata in leaves, and root hairs in roots. In old stems cork replaces the epidermis.
In the figure : The outer layer protects, absorbs and controls gas exchange.
Rule 1: The epidermis protects the plant — It forms a continuous cover that reduces water loss, blocks injury and keeps microbes out.
- Easy : A thick cuticle helps desert plants lose less water.
- Medium : An aquatic plant does not need a thick cuticle because it is surrounded by water.
- Exam-type : The cuticle and epidermis stop harmful microbes from entering.
Rule 2: Special parts of the epidermis do special jobs — Stomata exchange gases and release water vapour (transpiration). Root hairs increase the surface area for absorption. Cork cells are dead, tightly packed and impermeable.
- Easy : Stomata let in carbon dioxide for photosynthesis and release water vapour in transpiration.
- Medium : Root hairs are tiny outgrowths of root epidermal cells that absorb water and minerals.
- Exam-type : Cork forms the bark of old stems and protects the inner tissue.
Epidermis = outer cover; cuticle = wax; stomata = pores; root hairs = absorption; cork = bark.
Saying that the epidermis transports food. Transport is done by phloem and xylem, not by the epidermis.
Memory clue: E-C-S-R-C — Epidermis covers, Cuticle waterproofs, Stomata breathe, Root hairs absorb, Cork protects.
Spot the difference
| Structure | Where | Job |
|---|---|---|
| Cuticle | Over the epidermis | Waterproof wax layer |
| Stomata | Leaf epidermis | Gas exchange and transpiration |
| Root hair | Root epidermis | Absorbs water and minerals |
Practice questions
- 1Which is the outermost layer of the plant body?
- 2What is the cuticle made of?
- 3What are stomata?
- 4Why do desert plants have a thick cuticle?
- 5How do root hairs help a plant?
- 6Why is cork a better covering for old stems?
- 7A leaf had no stomata. Which two processes would be affected?
- 8A water plant has a thin cuticle but a desert plant has a thick one. Explain.
Show answers (try them yourself first)
- 1The epidermis.
- 2Cutin, a waxy substance.
- 3Tiny pores in the leaf epidermis for gas exchange and release of water vapour.
- 4To reduce water loss in dry surroundings.
- 5They increase the surface area to absorb water and minerals.
- 6Its cells are dead and tightly packed and are impermeable to water and gases.
- 7Gas exchange and transpiration.
- 8A water plant has no problem of water loss, whereas a desert plant must save water.
Supporting tissues: parenchyma, collenchyma, sclerenchyma
A tent needs poles for support but also flexible ropes, while a steel gate is hard and rigid. In the same way, plants use soft, flexible and hard tissues for different kinds of support.
The ground tissue of a plant has three simple permanent tissues. Parenchyma has living, thin-walled, loosely packed cells that store food and, if green, do photosynthesis. Collenchyma has living cells with corners thickened by pectin and gives flexible support. Sclerenchyma has dead cells with walls thickened by lignin and gives hardness and strength.
In the figure : Soft, flexible and hard support in a plant.
Rule 1: Simple permanent tissues are made of one kind of cell — Parenchyma, collenchyma and sclerenchyma are each made of only one kind of cell.
- Easy : Parenchyma stores food in the potato.
- Medium : Collenchyma in young stems and tendrils lets them bend without breaking.
- Exam-type : Sclerenchyma makes the husk of a coconut and the shell of a walnut hard.
Rule 2: Match the wall material to the job — Pectin gives flexibility, and lignin gives hardness.
- Easy : Fresh twigs bend because of collenchyma, but dry twigs snap when they are hard and brittle.
- Medium : Air spaces in parenchyma help water plants float.
- Exam-type : If all the flexible tissue in a young stem were replaced by sclerenchyma, the stem would be stiff and break in strong wind.
Parenchyma = store; collenchyma = flexible; sclerenchyma = hard. Pectin bends, lignin hardens.
Thinking that all three support tissues are alive. Mature sclerenchyma cells are dead.
Memory clue: P-C-S — Parenchyma = Pack food, Collenchyma = Can bend, Sclerenchyma = Strong and stiff.
Spot the difference
| Tissue | Cells | Job |
|---|---|---|
| Parenchyma | Living, thin walls | Stores food; photosynthesis; floating |
| Collenchyma | Living, corners thick with pectin | Flexible support |
| Sclerenchyma | Dead, lignin walls | Hardness and strength |
Practice questions
- 1Which tissue stores food in a plant?
- 2Which substance thickens the walls of sclerenchyma?
- 3Name the three simple permanent tissues.
- 4Why can a green twig bend but a dry twig snap?
- 5Why is parenchyma important for water plants?
- 6What gives coconut husk its toughness?
- 7A coriander stalk is soft and a coconut fibre is tough. Explain using the tissues involved.
- 8If the soft tissue in a young stem were replaced with sclerenchyma, what would happen in strong wind?
Show answers (try them yourself first)
- 1Parenchyma.
- 2Lignin.
- 3Parenchyma, collenchyma and sclerenchyma.
- 4A green twig has collenchyma, which is flexible; a dry twig is hard and brittle.
- 5Its air spaces help the plant float and it also stores food.
- 6Sclerenchyma, which has dead cells with thick lignin walls.
- 7Coriander stalk has collenchyma and parenchyma, which are soft and flexible; coconut fibre has sclerenchyma, which is hard.
- 8The stem would become stiff and brittle and would be more likely to break.
Conducting tissues, tissue systems and totipotency
A city has water pipes that carry water to homes and delivery vans that carry food around. A plant also has two transport systems running through its body.
Xylem carries water and minerals from roots to other parts. It has tracheids, vessels, xylem parenchyma and fibres, and most of its cells are dead. Phloem carries food from the leaves to all parts. It has sieve tubes, companion cells, phloem parenchyma and fibres. Plants have three tissue systems: dermal, ground and vascular.
In the figure : Xylem takes water up; phloem moves food around.
Rule 1: Xylem and phloem are complex tissues that move different things — They are called complex because they contain more than one type of cell working together.
- Easy : Xylem carries water and minerals up from roots, helped by the pull of transpiration.
- Medium : Phloem carries food from leaves to roots and other parts through sieve tubes controlled by companion cells.
- Exam-type : If a ring of bark (with phloem) is removed from a branch, food collects above the cut and the bark bulges there.
Rule 2: Plant cells can be totipotent — Some mature cells, grown in a nutrient medium, can divide and form a whole new plant. This was shown by F. C. Steward in 1958 using carrot phloem cells.
- Easy : Steward's cells first formed a mass of unspecialised cells (dedifferentiation).
- Medium : Then they redifferentiated into roots, stems and finally a whole carrot plant.
- Exam-type : Agrobacterium tumefaciens causes crown gall disease but can also carry genes into plant cells, which is used in tissue culture and genetic engineering.
Xylem = water up; phloem = food; the three tissue systems are dermal, ground and vascular.
Mixing up the two. Xylem (mostly dead) moves water; phloem (living) moves food.
Memory clue: X-W, P-F — Xylem = Water, Phloem = Food.
Spot the difference
| Point | Xylem | Phloem |
|---|---|---|
| Carries | Water and minerals | Food from leaves |
| Main parts | Tracheids, vessels, fibres, parenchyma | Sieve tubes, companion cells, fibres, parenchyma |
| Living or dead | Mostly dead | Mostly living |
Practice questions
- 1Which tissue carries water in plants?
- 2Name the three tissue systems of a plant.
- 3What are companion cells?
- 4A farmer removes a ring of bark from a branch. Why does the part above the cut swell?
- 5What does 'totipotent' mean?
- 6How does transpiration help xylem?
- 7Describe what Steward did in 1958 and what he found.
- 8Explain why Agrobacterium is useful for scientists even though it causes crown gall.
Show answers (try them yourself first)
- 1Xylem.
- 2Dermal, ground and vascular tissue systems.
- 3Cells that control the work of sieve tube cells.
- 4The phloem is cut and food coming down from the leaves collects above the cut.
- 5A cell that can divide and form a whole organism.
- 6Transpiration creates a pull that draws water up through the xylem.
- 7He grew single carrot phloem cells in a nutrient medium; they formed a whole carrot plant.
- 8It can carry genes into plant cells, which is used in genetic engineering and tissue culture.
Epithelial and connective tissues
Your skin keeps you covered, the food pipe has a lining, and blood runs all through your body. Your body has four main kinds of tissue doing such different jobs.
Animal tissues are of four types: epithelial, connective, muscular and nervous. Epithelial tissue covers the body and lines organs, with cells packed closely. Connective tissue joins and supports other tissues and includes blood, bone, cartilage, tendons and ligaments. Its cells lie scattered in a non-cellular matrix.
In the figure : Four tissues, four main jobs.
Rule 1: Epithelial tissue forms covers and linings — Its tightly packed cells block microbes and water loss. The type of cell matches the job.
- Easy : Thin flat cells in a single layer line the lungs and blood vessels and allow quick diffusion of gases.
- Medium : Many layers of flat cells in the skin and mouth protect against injury.
- Exam-type : Gland cells in salivary and sweat glands secrete substances, and cells with cilia in the nose and ear sense smell and sound.
Rule 2: Connective tissue matches its matrix to the job — Blood has a liquid matrix, bone a hard one and cartilage a soft, jelly-like one.
- Easy : Blood: plasma is about 55% and formed elements about 45% of the volume; red cells carry oxygen with haemoglobin, platelets help clotting and white cells fight infection.
- Medium : Bone is hard because its matrix has calcium and phosphorus compounds; cartilage is soft and flexible, like the outer ear.
- Exam-type : Tendons join muscle to bone; ligaments join bone to bone.
Epithelial = cover and line; connective = join and support. Tendon: muscle–bone; ligament: bone–bone.
Saying that blood is not a tissue. Blood is a fluid connective tissue.
Memory clue: T-M-B — Tendon = Muscle to Bone; L-B-B — Ligament = Bone to Bone.
Spot the difference
| Connective tissue | Matrix | Job |
|---|---|---|
| Blood | Liquid plasma | Transport, clotting, defence |
| Bone | Hard, with calcium and phosphorus | Support and protection |
| Cartilage | Soft, jelly-like | Flexible support, cushion |
Practice questions
- 1Name the four types of animal tissue.
- 2Which tissue covers the body and lines organs?
- 3What joins a muscle to a bone?
- 4Why are epithelial cells packed tightly?
- 5Why is blood called a connective tissue?
- 6How are bone and cartilage different?
- 7A 20 mL blood sample has 55% plasma. What is the volume of the formed elements?
- 8A footballer tears the tissue joining the thigh bone to the shin bone at the knee. What is it called?
Show answers (try them yourself first)
- 1Epithelial, connective, muscular and nervous.
- 2Epithelial tissue.
- 3A tendon.
- 4To block microbes and prevent loss of water.
- 5Because it joins and supports parts of the body and has cells in a liquid matrix.
- 6Bone is hard because of calcium and phosphorus compounds in its matrix; cartilage is soft and flexible.
- 745% of 20 mL = 9 mL.
- 8A ligament.
Muscular and nervous tissues
A cricket player moves quickly, your heart beats on its own all day, and your hand pulls away from a hot pan before you think. Muscle and nerve tissue make all this possible.
Muscular tissue makes movement by contracting. Skeletal muscle is striped and voluntary. Smooth muscle has spindle-shaped cells and is involuntary. Cardiac muscle is branched, is found only in the heart and works without tiring. Nervous tissue is made of neurons that receive, process and send signals.
In the figure : Three kinds of muscle in the body.
Rule 1: Match each muscle type to its features — Skeletal fibres are long, cylindrical, unbranched and multinucleate; smooth cells are spindle-shaped with one nucleus and no stripes; cardiac fibres are branched with one nucleus.
- Easy : Writing and lifting a bag use skeletal muscle (voluntary).
- Medium : Movement of food in the gut uses smooth muscle (involuntary).
- Exam-type : The heartbeat is cardiac muscle (involuntary and never tiring).
Rule 2: Nerve cells control and coordinate — A neuron has a cell body with the nucleus, dendrites that receive signals, and an axon that carries the message to the axon terminals.
- Easy : You pull your hand from a hot object quickly because nervous tissue sends signals fast.
- Medium : During exercise the brain signals the heart to beat faster.
- Exam-type : Muscles cannot work by themselves; they receive instructions from nervous tissue.
Skeletal = striped and voluntary; smooth = spindle and involuntary; cardiac = branched, only in heart. Neuron: dendrite in, axon out.
Thinking that all involuntary muscle is cardiac muscle. Smooth muscle is also involuntary.
Memory clue: D-A-C — Dendrites Download (receive), Axon Away (sends), Cell body Controls.
Spot the difference
| Muscle | Cell shape | Control |
|---|---|---|
| Skeletal | Long, cylindrical, striped, many nuclei | Voluntary |
| Smooth | Spindle-shaped, one nucleus, no stripes | Involuntary |
| Cardiac | Branched, one nucleus, only in heart | Involuntary |
Practice questions
- 1Which muscles do we control at will?
- 2Where is cardiac muscle found?
- 3What is the nerve cell called?
- 4Which part of a neuron receives signals from other neurons?
- 5Why does the heart beat faster during exercise?
- 6Which muscle moves food through the gut?
- 7A slide shows long cylindrical cells with many nuclei and stripes. Which muscle is it?
- 8A slide shows spindle-shaped cells with one nucleus and no stripes. Which muscle is it?
Show answers (try them yourself first)
- 1Skeletal muscles.
- 2In the heart only.
- 3A neuron.
- 4The dendrites.
- 5The brain sends signals to the heart through nervous tissue.
- 6Smooth muscle.
- 7Skeletal muscle.
- 8Smooth muscle.
Musculoskeletal system, joints and skeleton
A tent frame holds the cloth in shape, hinges let a door swing one way, and a ball joint lets a toy arm turn in all directions. The body's skeleton and joints work in very similar ways.
The musculoskeletal system is made of bones, muscles, joints, cartilage, tendons and ligaments. It supports the body, protects organs and allows movement. A joint is where two or more bones meet. Ball-and-socket joints allow movement in many directions, hinge joints in one plane, pivot joints turn, and fixed joints do not move.
In the figure : Four types of joints and where they are found.
Rule 1: Match the joint type to its movement — The shape of the bone ends decides the movement.
- Easy : Shoulder and hip: ball-and-socket, movement in many directions.
- Medium : Elbow and knee: hinge, bending in one plane.
- Exam-type : Between the skull and the top of the spine, a pivot joint lets you turn your head; skull bones are joined by fixed joints.
Rule 2: Parts of the skeleton and their jobs — The skull protects the brain, the backbone is made of vertebrae with discs between them, and the 12 pairs of ribs (24 ribs) form a cage that protects the heart and lungs.
- Easy : Cartilage joins the ribs to the breastbone so that the rib cage can expand and contract in breathing.
- Medium : When a muscle contracts, its tendon pulls on the bone and the joint moves.
- Exam-type : Bones are about 12–15% of the body weight; muscle makes up 40–50% in males.
Ball and socket = many directions; hinge = one plane; pivot = turn; fixed = no movement. 12 pairs of ribs = 24.
Mixing up tendon and ligament. A tendon joins muscle to bone and a ligament joins bone to bone.
Memory clue: B-H-P-F — Ball (shoulder), Hinge (knee), Pivot (neck), Fixed (skull).
Spot the difference
| Joint | Example | Movement |
|---|---|---|
| Ball and socket | Shoulder, hip | Many directions |
| Hinge | Elbow, knee | One plane |
| Pivot / Fixed | Neck / Skull | Turns / None |
Practice questions
- 1Which joint allows movement in many directions?
- 2How many pairs of ribs does a human have?
- 3What protects the brain?
- 4Why are the ribs joined to the breastbone by cartilage?
- 5What happens at a joint when a muscle contracts?
- 6Name the joint at the elbow and the type of movement it allows.
- 7A person weighs 60 kg and the bones are 12% of the body weight. Find the weight of the bones.
- 8A dancer rotates her arm in a full circle. Which joint is mainly involved?
Show answers (try them yourself first)
- 1Ball-and-socket joint.
- 212 pairs, that is 24 ribs.
- 3The skull.
- 4Cartilage is flexible, so the rib cage can expand and contract in breathing.
- 5The tendon pulls the bone and the joint moves.
- 6A hinge joint, which allows movement in one plane.
- 760 × 12 ÷ 100 = 7.2 kg.
- 8The ball-and-socket joint at the shoulder.
Musculoskeletal system, joints and skeleton
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