Tissues and Supporting Systems – SS1 Biology Lesson Note (Second Term)

A tissue is a group of similar cells that carry out a specific function, and the skeleton is the framework that supports and protects the soft parts of an animal’s body.

• Tissues: all organisms, plants and animals, need tissues to carry out life processes.
• Skeleton: gives support, shape and protection to soft tissues and organs.
• Position in man: the skeleton forms the central core of the body, covered by muscles, blood vessels and skin.

Behavioural objectives

1. Define tissue and skeleton, and name the three forms of skeletal material.
2. Distinguish between bone and cartilage.
3. Describe hydrostatic skeleton, exoskeleton and endoskeleton with examples.
4. Identify the parts of the axial and appendicular skeletons and state their functions.
5. Name the supporting tissues in plants and state their functions.

What are the forms of skeletal material?

There are three forms of skeletal material in animals: chitin, cartilage and bone.

What is chitin?

Chitin is a tough, non-living material that forms the hard outer covering of arthropods.

• Where found: arthropods (invertebrates) such as insects, crabs and spiders.
• Structure: a series of plates covering or surrounding the animal.
• Properties: very tough, light and flexible.
• Strengthening: tanned proteins harden it, and calcium carbonate strengthens it in aquatic crustaceans such as crabs.

What is cartilage?

Cartilage is a tough, flexible skeletal tissue made of living cells in a firm matrix penetrated by connective tissue fibres.

• Chondroblasts: living cells that secrete the matrix.
• Lacunae: spaces in the matrix that later enclose the cells.
• Chondrocytes: the name for chondroblasts once enclosed in lacunae.
• Function: acts as a shock absorber between bones during movement, because it has great tensile strength.
• Where found: mainly in mammals and cartilaginous fishes such as sharks.

What are the types of cartilage?

There are three types of cartilage in mammals: hyaline, white fibrous and yellow elastic cartilage.

• Hyaline cartilage: the most common type, found on the surface of movable joints, in the trachea and bronchi, and in the nose.
• White fibrous cartilage: tougher than hyaline cartilage, found in the intervertebral discs of the vertebral column.
• Yellow elastic cartilage: found in the external ear (pinna) and the epiglottis, the flap that covers the trachea during swallowing.

What is bone?

Bone is the major component of the skeletal system, made of living cells, protein fibres and minerals.

• Osteocytes: the living bone cells.
• Collagen: the protein fibres in bone.
• Minerals: calcium carbonate and calcium phosphate, which are non-living and make up about two-thirds of the mass of bone.
• Result: bone is strong and rigid, unlike cartilage.
• Blood supply: bones are highly vascularised (they have many blood vessels).

What is ossification?

Ossification is the hardening of cartilage into bone through the addition of minerals.

1. The skeleton of a young vertebrate embryo is made of cartilage.
2. As the embryo grows, bone cells (osteocytes) replace cartilage cells.
3. Minerals are added and the cartilage hardens into bone.

What is the difference between bone and cartilage?

• Bone: a rigid skeletal tissue containing living cells and a hard mineral matrix.
• Cartilage: a flexible skeletal tissue made mainly of living cells in a firm matrix.

What are the types of skeleton in animals?

There are three types of skeleton in animals: hydrostatic skeleton, exoskeleton and endoskeleton.

What is a hydrostatic skeleton?

A hydrostatic skeleton is a fluid-filled body supported by pressure, found in soft-bodied animals.

• Examples: earthworm and sea anemone.
• Body wall: muscular, and surrounds a body space filled with fluid.
• Action: the muscles contract and press on the fluid, and the fluid pressure supports the body and changes its shape.

What is an exoskeleton?

An exoskeleton is the outer skeleton of arthropods, made mainly of chitin.

• Origin: secreted by the cells covering the body.
• Functions: supports the animal against gravity and enables it to move about.
• Moulting (ecdysis): the periodic shedding of the old exoskeleton.
• Growth: the animal grows rapidly while the new exoskeleton is still soft and extensible.
• Examples: insects such as grasshoppers, and crabs.

What is an endoskeleton?

An endoskeleton is the internal skeleton of vertebrates, made mainly of bones.

• Growth: bones grow steadily as the animal grows, so there is no moulting.
• Ligaments: tough, flexible fibres that attach bones at movable joints.
• Tendons: attach muscles to bones to give posture and bring about movement.
• Bones: come in many sizes and shapes.

What are the functions of the skeleton?

The skeleton supports the body, protects organs and makes movement possible.

1. It supports the body of the organism.
2. It acts as the framework of the body.
3. It protects delicate organs such as the heart and brain.
4. It is used for locomotion through the action of the limbs.
5. It helps breathing, because the ribs move during breathing.
6. It produces blood cells in the bone marrow.

How is the skeleton of vertebrates classified?

The skeleton of vertebrates such as fish, frogs, lizards, birds and man is made of bones and cartilage, and has two parts: axial and appendicular.

• Axial skeleton: the skull, ribs, sternum and vertebral column.
• Appendicular skeleton: the limb girdles (pectoral and pelvic) and the limbs (fore and hind).

What is the axial skeleton?

The axial skeleton is the central part of the skeleton, made up of the skull, vertebral column, ribs and sternum.

What is the skull?

The skull is the bony structure of the head, made of flat bones joined by suture joints.

• Cranium: the brain-box.
• Facial skeleton: the bones of the face.
• Jaws: the maxilla (upper) and the mandible (lower).

Functions of the skull:

1. It protects the brain.
2. It protects the olfactory organ, eyes, middle ear and inner ear.
3. It gives shape to the head.
4. It bears the teeth.

What is the vertebral column?

The vertebral column is the backbone, which protects the spinal cord.

• Vertebrae: the individual bones, built on a similar basic pattern.
• Groups: five groups, namely cervical, thoracic, lumbar, sacral and caudal.
• Joining: held together by strong ligaments.
• Intervertebral discs: compressible cartilage pads between the vertebrae.

What are the parts of a typical vertebra?

• Neural canal: passage for the spinal cord.
• Neural spine: projects upward and backward, for attachment of muscles.
• Transverse processes: for attachment of muscles and ligaments.
• Centrum: a solid bony piece below the neural canal.
• Zygapophyses: surfaces that join successive vertebrae.
• Prezygapophysis: faces inward and upward.
• Postzygapophysis: faces outward and downward.

How many vertebrae are in each region?

What are the cervical vertebrae?

The cervical vertebrae are the neck vertebrae, and the first two are called the atlas and the axis.

• Atlas (first): large neural canal, flat and broad transverse processes, and a short neural spine that may be absent.
• Atlas, other features: has a vertebrarterial canal for blood vessels, and has no centrum.
• Atlas, function: permits nodding of the head.
• Axis (second): broad, flat centrum, large flat neural spine, reduced transverse processes and a vertebrarterial canal.
• Axis, odontoid process: the projection through which the axis articulates with the atlas.
• Axis, functions: permits turning or twisting of the head, and forms a pivot joint with the atlas.

What are the thoracic vertebrae?

The thoracic vertebrae are the chest vertebrae, which carry the ribs.

• Features: long, prominent neural spine, a pair of short transverse processes, a large neural canal and a large cylindrical centrum.
• Rib surfaces: special surfaces for attachment of the ribs.
• Functions: aid attachment of ribs, assist breathing, and give attachment to muscles of the shoulder and back.

What are the lumbar vertebrae?

The lumbar vertebrae are the vertebrae of the lower back, with large, thick centrums.

• Features: large flat transverse processes, broad flat neural spine, large thick centrum and well-developed zygapophyses.
• Extra projections: anapophysis and metapophysis, in pairs.
• Functions: give attachment to abdominal muscles and bear considerable body weight.

What are the sacral vertebrae?

The sacral vertebrae fuse together to form a single bony mass called the sacrum.

• Features: narrow neural canal, reduced neural spine and large centrums.
• First sacral vertebra: has a pair of large, wing-like transverse processes, unlike the other four.
• Neural canal: becomes narrower in the lower four vertebrae.
• Function: joins the pelvic girdle to give support, rigidity and strength.

What are the caudal vertebrae?

The caudal vertebrae are the tail vertebrae, which fuse to form the coccyx in man.

• Features: no neural spine, no neural canal and no transverse process.
• Appearance: a solid rectangular mass of bone.
• Functions: support the tail and give attachment to tail muscles.

What are the ribs?

The ribs are long, semi-circular rods that connect the thoracic vertebrae to the sternum.

• Position: in the chest region.
• Number in man: 12 pairs.
• Parts of a typical rib: head, neck and body.
• True ribs: the first seven pairs, joined directly to the sternum by costal cartilage.
• False ribs: the next five pairs.
• Ribs 8 to 10: each is attached by costal cartilage to the rib above, and they share a common attachment to the sternum.
• Floating ribs: the 11th and 12th pairs, which have no connection to the sternum.
• Functions: form a cage that protects the lungs and heart, and assist breathing.

What is the appendicular skeleton?

The appendicular skeleton is made up of the limb girdles and the limbs.

What is the pectoral girdle?

The pectoral girdle is the shoulder girdle, made of two halves held in place by muscles.

• Scapula: flat and triangular, with a hollow at its tip called the glenoid cavity.
• Coracoid: fixed to the scapula.
• Clavicle: a small rod of bone attached by a ligament, joining the sternum to the scapula.
• Shoulder joint: the glenoid cavity joins the head of the humerus.
• Functions: gives attachment to muscles and ligaments, and gives firm support to the forelimbs.

What is the pelvic girdle?

The pelvic girdle is the hip girdle, made of two halves joined to each other at the front and to the sacrum at the back.

• Ilium: one of the three bones in each half.
• Ischium: the second bone.
• Pubis: the third bone.
• Acetabulum: the depression formed by the three bones, which joins the head of the femur to form the hip joint.

What are the limbs?

The limbs are the fore (upper) and hind (lower) limbs, built on the same basic plan in most vertebrates.

• Basic plan: one long bone, then two long bones, then small bones, ending in five digits.

• Humerus: the upper arm bone, which meets the radius and ulna at the elbow joint.
• Ulna: the longer of the two forearm bones.
• Fingers in man: each has three phalanges, except the thumb, which has two.
• Femur: the thigh bone, the largest and longest bone in the body.
• Condyles: two rounded projections at the lower end of the femur, which form the knee joint with the tibia.
• Patella: a small flat bone in front of the knee joint.
• Tibia: the longer and larger bone of the lower leg.
• Toes in man: each has three phalanges, except the big toe, which has two.

Why do plants need supporting tissues?

Supporting tissues give plants a definite shape, strength and rigidity, and help them resist external forces such as wind and water.

1. Definite shape.
2. Strength.
3. Rigidity.
4. Resistance against external forces such as wind and water.

What are the supporting tissues in plants?

There are five supporting tissues in plants: parenchyma, collenchyma, sclerenchyma, xylem and phloem.

What is parenchyma?

Parenchyma is the most common and abundant plant tissue, made of living cells with cellulose walls and many air spaces.

• Support: gives firmness and turgidity to stems, for example the hibiscus stem.
• Storage: stores food and water.
• Food making: takes part in food synthesis in the leaf mesophyll.

What is collenchyma?

Collenchyma is a tissue of living, elongated cells that are thickened at the corners.

• Support: provides strength and support in young growing plants.
• Flexibility: gives flexibility and resilience to the plant.

What is sclerenchyma?

Sclerenchyma is a tissue of thick-walled cells containing cellulose and lignin, rich in fibres.

• Strength: provides strength, rigidity, hardness and support.
• Flexibility: the fibres give some flexibility to the plant.

What is xylem?

Xylem is a vascular tissue found in the roots, stems and leaves.

• Support: provides support, strength and shape to the plant.
• Conduction: carries water and mineral salts from the roots to the leaves.

What is phloem?

Phloem is a vascular tissue found in the vascular bundles of the roots, stems and leaves.

• Conduction: carries manufactured food from where it is made to where it is used or stored.
• Support: helps to support the whole plant.

Evaluation

1. Define tissue and skeleton.
2. Name the three forms of skeletal material in animals.
3. State two differences between bone and cartilage.
4. State the function of the atlas and the axis.
5. Name the three bones that make up each half of the pelvic girdle.

Assignment

Answer all the questions below in your exercise book.

1. ___ is a non-living skeletal material. A. chondroblasts B. osteocyte C. elastic cartilage D. chitin
2. The surface for joining successive vertebrae is called the A. neural spine B. zygapophysis C. transverse process D. neural canal
3. The canal for the passage of blood vessels in the cervical vertebrae is called the A. neural canal B. cervical canal C. vertebrarterial canal D. kyphosis
4. Which of these animals has no endoskeleton? A. dog B. snake C. shark D. earthworm
5. The most abundant supporting tissue in plants is A. sclerenchyma B. parenchyma C. xylem D. phloem
6. (a) What is ecdysis? (b) Mention two animals in which it occurs.
7. Differentiate between (a) bone and cartilage, (b) atlas and axis vertebrae.