Unit 1 – Cell Structure and Organisation 1.1 – Plant and Animal Cells, 1.2 – Specialised cells, tissues and organs

SUFEATIN SURHAN BIOLOGY 5090 2012

SYLLABUS CHECKLIST

Candidates should be able to:

a) examine under the microscope an animal cell (e.g. from fresh liver) and a plant cell (e.g. from Elodea, a

moss, onion epidermis, or any suitable, locally available material), using an appropriate temporary staining technique, such as iodine or methylene blue;

b) draw diagrams to represent observations of the plant and animal cells examined above;

c) identify, from fresh preparations or on diagrams or photomicrographs, the cell membrane, nucleus and

cytoplasm in an animal cell;

d) identify, from diagrams or photomicrographs, the cell wall, cell membrane, sap vacuole, cytoplasm,

nucleus and chloroplasts in a plant cell;

e) compare the visible differences in structure of the animal and the plant cells examined;

f) state the function of the cell membrane in controlling the passage of substances into and out of the cell;

g) state, in simple terms, the relationship between cell function and cell structure for the following:

absorption – root hair cells; conduction and support – xylem vessels; transport of oxygen – red blood cells;

h) identify these cells from preserved material under the microscope, from diagrams and from

photomicrographs;

i) differentiate cell, tissue, organ and organ system as illustrated by examples covered in sections 1 to 12,

15 and 16.

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What is Biology?

Biology is the study of life. Biology allows us to answer questions such as:

Various fields of study in Biology include:

Genetics: Study of heredity. Virology: Study of viruses. Entomology: Study of insects. Anatomy: Study of the structure of organisms. Botany: Study of plants. Zoology: Study of animals. Histology: Study of tissues. Mycology: Study of fungi.

The 8 characteristics of living things

M MOVEMENT: Animals move its whole body by using limbs or their equivalent. A plant moves only by growing part of itself towards or away from influences important to it.

E EXCRETION: The process involving the removal of metabolic waste products such as carbon dioxide, water, mineral salts and nitrogenous waste products. These substances will harm organisms if not removed.

R REPRODUCTION: The process of the production of new generation of offspring necessary for the survival of species.

I IRRITABILITY: The process of sensing and responding to stimuli or any changes in the immediate environment (light, sound, touch, pressure, temperature).

G GROWTH: An increase in the cell numbers, size, dry mass or volume of an organism as a result of converting absorbed food into living protoplasm. This may make an organism more complex or even change its form e.g. germination of a seed, caterpillar changing into a butterfly.

R RESPIRATION: The release of energy from the oxidation of food; the energy is used for movement, growth, reproduction, etc.

A ADAPTABILITY: Organisms have the ability to adjust and adapt themselves to changes in their environment.

N NUTRITION: The process where organisms take in food substances and convert them into the living protoplasm of the organism.

Cell, Basic unit of life

The cell is the structural and functional basic unit of

living organisms.

It is the simplest unit of life, basic unit of life or the simplest organized unit of living matter.

There are two major types of cells: 1. Prokaryotic cells: Cells in unicellular organisms

which exists singly as independent organisms showing all the characteristics of life e.g. amoeba, bacteria, paramecium.

2. Eukaryotic cells: Cells in multicellular organisms. These cells become modified for specific functions e.g. root hair cells, red blood cells, epithelial cells.

Living cells are made of protoplasm. The protoplasm of a cell consists of a cell membrane, cytoplasm and nucleus.

Protoplasm is the mass of living matter. It is a complex jelly like substance of which 70-90% is water while the rest consists of mineral salts and organic compounds. Chemical reactions take place here.

The cytoplasm contains structures which perform functions. They are known as organelles.

Organelles include nucleus, vacuoles, mitrochondrion, ribosomes, endoplasmic reticulum, golgi body, centrioles and chloroplasts.

Cells can only be seen under high magnification. Cells have many features in common but their precise structure is closely related to the work they do.

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Cell Structure

All cells have the following structural features in common:

Structure Function

Cell membrane - made up of two layers of lipids and proteins

Selectively controls the passage of substances entering and leaving the cell (selectively permeable) General rule: Small molecules can enter easily e.g. water (osmosis), oxygen, carbon dioxide (diffusion); Large molecules cannot e.g. proteins and starch

PR

OT

OPLA

SM

( Liv

ing m

att

er

)

Cytoplasm

- a jelly-like substance within the cell - consists of 90% water with dissolved salts and sugars; fats and proteins are suspended in it

Site of chemical reactions (metabolic reactions) where organelles can be found e.g. nucleus, mitochondria Temporary food storage e.g. oil globules, starch granules (in plants only)

Nucleus (pl: nuclei)

- largest organelle (visible in the light microscope) - has DNA, enclosed by nuclear membrane - In non-dividing cells, DNA forms long chromatin threads - In dividing cells, DNA condenses (coils up) into visible chromosomes

Contains chromosomes which carry genetic information of the cell; Chromosomes possess genes for programming the cytoplasm to manufacture particular proteins Controls all chemical reactions within the cell and cell division

Mitochondrion (pl: Mitochondria)

- smaller sized organelle (visible only with electron microscope)

Site of respiration

Ribosomes

- Very tiny round organelles present in the cytoplasm

Site of synthesis of proteins from amino acids

Plant cells have the following additional structures:

Structure Function

Cellulose cell wall

- Cellulose form fibres that criss-cross over one another to form a very strong covering of the cell.

Fully permeable membrane i.e. allows any substance to pass through it Supports non-woody plant organs (by turgor pressure) Supports and protects the cell (prevents from bursting) and give shape to cell

A large, central vacuole / Sap Vacuole

- contains a solution called cell sap consisting of 90% water and dissolved salts and sugars - separated from the cytoplasm by the vacuolar membrane = tonoplast - Dividing cells do not have a vacuole

Important for osmoregulation (regulation of water content by osmosis) For food storage Helps to maintain the shape of the cell

Chloroplasts

- small organelles in the cytoplasm

Contains green pigments, chlorophyll, for absorption of sunlight required for photosynthesis

Summary

ANIMAL CELL PLANT CELL

SIMILARITIES

Cell membrane present

Cytoplasm present

Nucleus present

Mitochondria present

Ribosome present

DIFFERENCES

Cell wall absent Cell wall present

Sap vacuole absent

* Have many temporary vesicles

Sap vacuole present

Chloroplasts absent

Chloroplasts present

Starch granules absent; glycogen granules usually

present

Starch granules present

Tonoplast is absent

Tonoplast, a thin membrane that

surrounds the sap vacuole is present

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Specialised cells, tissues and organs

In unicellular organisms, one cell must be able to carry out all functions of a living organism.

In multicellular organisms, cells are usually modified to carry out one main function. The appearance of the cell will vary depending on what that main function is.

There is a relationship between the structure of a cell and its function. This specialisation of cells to carry out particular functions in an organism is referred to as ‘division of labour’.

The Root Hair Cell

Functions:

Absorption of water from the water film surrounding the soil particle by osmosis.

Allows simple diffusion of dissolved mineral salts in the soil solution to pass into the root hair.

Absorb minerals that are present in low concentration in the soil by active transport.

Adaptations:

1. It has a long, tubular shape.

- Able to form very close contact with the water film surrounding many soil particles (able to penetrate between the soil particles).

- Greatly increases the surface area of the cell available for uptake of water and mineral salts (due to its shape and large number of root hairs).

2. Has a very concentrated cell sap in its vacuole - Increases the water potential gradient between

the soil water and the root hair cell so that water will tend to move into the cell by osmosis.

The Xylem vessel

Functions: To conduct or transport water and mineral salts

from roots to stems, leaves, flowers and fruits.

To provide mechanical support for the parts of the plant above the ground.

Adaptations:

1. Conduction:

- Xylem vessels are stacked end-to-end and the end walls are digested away to form long, continuous, narrow tubes, stretching from the roots, through the stem to the leaves.

- They have hollow lumen i.e. no cytoplasm, allowing water and its dissolved mineral salts to pass through unimpeded (no obstruction). This is why xylem vessels are dead cells.

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2. Support: - The cell walls of xylem vessels are strengthened

by the strong, rigid and waterproof substance called lignin. As the lignin in the walls build up, it eventually kills the xylem vessels. Hence, the hollow lumen.

- Xylem vessels are part of the vascular bundles which run through the stem of plants like steel reinforcements in concrete pillars. They help to resist bending strains caused by the wind.

The Red Blood Cells or Erythrocyte

FUNCTION: To carry oxygen around the body in the form of

oxyhaemoglobin. ADAPTATIONS: 1. The cytoplasm in red blood cells contains the

pigment haemoglobin. Haemoglobin combines with oxygen in the lungs to become oxyhaemoglobin. This is a reversible process.

2. The absence of nucleus (enucleated) means space for more haemoglobin enabling more oxygen to be transported increasing their efficiency.

3. The cells are small and there are many of them, so they have a very large surface area for oxygen absorption.

4. They have a flat, biconcave shape making their surface area for absorption (by diffusion) even larger.

5. They are flexible, allowing them to be pushed easily through the small blood vessels i.e. capillaries whereby they become bell-shaped.

Muscle cells

FUNCTION: To cause movement when they

contract.

(Contraction brings about a decrease in length of the cell. Muscles can only do work when they contract, never when they relax)

ADAPTATIONS: 1. They are long and thin, allowing many to work side-

by-side for greater force, or to form a contractile network.

2. Their cytoplasm contains many mitochondria which are responsible for releasing energy within a cell and necessary here to bring about contraction.

Cells, Tissues, Organ System and Organism

One cell working on its own would achieve very

little in an individual plant or animal, so it is common to find many similar cells lying side-by-side and working together, performing the same function to increase efficiency.

Tissues

Many similar cells working together and performing

the same function is known as a tissue.

ANIMAL TISSUES (based on humans) Types of

tissue Contents Main Function

Epithelial tissue

Layers of cells placed end to end

To cover the external surface. To serve as a protective lining. To line tubes and spaces and form the skin.

Skeletal tissue

Hard material To support the body and permit movement.

When longitudinal

muscles contract, they

become short

When circular muscles

contract, they become

smaller

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Blood tissue Runny fluid To carry oxygen and food round the body.

Nervous tissue

Brain and nerve cells

To conduct nerve impulses and coordinate messages.

Muscular tissue

Bundles of muscles in arms, heart, etc.

To bring about movement for locomotion, breathing peristalsis.

Connective tissue

Bone, cartilage, blood

Joins body structure together. Provides protection and support. Has ability to store and transport materials.

PLANT TISSUES (based on flowering plants) Types of

tissue Contents Main Function

Epithelial tissue

Layers of cells

To cover surface of plants. To protect from physical damage and infection. To reduce water loss.

Photosynthetic tissue

Cells with chloroplasts

To provide cells with chlorophyll. To absorb sunlight. To perform photosynthesis.

Packing tissue Round balloon-like cells

To fill in spaces inside the plant for mechanical support.

Vascular tissue

Xylem

Cambium

Phloem

Xylem vessels Cambium cells Sieve tubes, sieve cells and companion cells

To transport water and mineral salts from roots to all parts of the plant. To provide mechanical support to plant. New tissue growth in the cambium. To transport food substances.

Organ

Several different tissues working together to

perform a particular function.

Organism Type of organs Function

ANIMAL

Alimentary canal To digest food

Nose, trachea, lungs Gaseous exchange

Heart and blood

vessels

Transport oxygen and

dissolved food

substances

PLANT Leaf

Photosynthesis

Transpiration

Flower Reproduction

Organ system

An organ system is a collection of different organs

working together to perform a particular function.

ORGAN SYSTEM IN ANIMALS

System Main organs of

system Main Function

Digestive system

Oesophagus, stomach, duodenum, ileum, colon, liver, pancreas

To digest the ingested food To absorb digested food To expel undigested food

Respiratory system

Trachea and lungs

To take in oxygen To get rid of carbon dioxide

Circulatory system

Heart, veins, arteries, capillaries

To carry oxygen and food around the body To regulate body temperature

Excretory system

Kidneys, urinary bladder, liver, lungs, skin

To get rid of toxic metabolic products

Sensory system

Eyes, ears, nose To detect stimuli

Nervous system

Brain, spinal cord

To control and coordinate body movements To conduct impulses from one part of the body to another

Muscular system

Muscles, skeleton

To move parts of the body

Skeletal system

skeleton To support the body To protect internal organs

Reproductive system

Testes, ovaries, uterus

To produce gametes To protect and nourish the embryo during development in the uterus

ORGAN SYSTEM IN PLANTS

The sepals, stamens, petals and carpels in a flower

make up the reproductive system of a plant.

Organism

A collection of organ system working together.

Example in human: Digestive system, circulatory system, respiratory system, urinary system, nervous system, reproductive system all combine together to form an organism.

The increasing order of cell organisation found within any living

organism is:

Cell → Tissues → Organs → Organ systems → Organisms

SURFACE AREA TO VOLUME RATIO

All animals need to take in oxygen and food substances from the environment and to eliminate carbon dioxide and other waste products from their bodies.

Small animals such as protozoa, jellyfish and flatworms carry out their exchanges by simple diffusion through their body surfaces. It is therefore important to study the relationship between surface area and volume in the living organism. This factor affects the rates of gaseous exchange, heat loss and loss of excretory products.

Notice that as the cube becomes bigger, the surface area does not increase in the same proportion as the volume.

The largest cube has the smallest surface area : volume ratio. Therefore, as the smaller the size of the cell or organism, the greater the surface area : volume ratio, the faster and more efficient the rate of diffusion of food and gases into the organism. It also means diffusion of waster products also diffuse out of the organism or cell at a faster rate.

As an object becomes larger, its surface area compared to its volume is smaller. Diffusion is no longer an effective way to transport materials to the inside. For this reason, there is a physical limit for the size of the cell, with the effectiveness of diffusion being the controlling factor. This explains why small organisms such as amoeba and bacteria undergo cell division when they grow too big.