GCSE level School Biology Notes: Introduction to cell organisation

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specialised cells ==> specific tissues ==> organs  ==> organ systems ==> complete multicellular animal or plant organism

Introduction to cell organisation of plants and animals explaining from cells to tissues to organs to organ systems to whole organism

Doc Brown's school biology revision notes

Index of notes on cell organisation (this page only)

1. Introduction and reminders about cells

2. Examples of the organisation of tissue cells

3. Examples of organ and gland cells

4. From tissues and organs to organ systems

5. More summary examples of tissues ==> organ as part of whole organism

1.  Introduction and reminders about cells

 Many organisms consist of a huge number of cells. (cell structure)

Most cells can be thought of as a unit of life surrounded and enclosed by an outer membrane of some sort.

 But, how are they organised to form e.g. a fully functioning animal?

 Cells are the building blocks of multicellular organisms.

 In the process called differentiation, cells become specialised to carry out a particular function e.g.

The derived specialised cells include:

Bone cells in skeletal systems.

Blood cells in the circulatory transport system.

Nerve cells in the nervous system.

Sperm cells and egg cells in the reproductive systems.

Differentiation happens during the growth and development of a multicellular organism.

Specialised cells form tissues, which can connect to form organs and these connect together to form organ systems.

Large multicellular organisms like animals have different organ systems for exchanging and transporting substances.

2. Examples of the organisation of tissue cells

A tissue is a group of similar specialised cells that work together to carry out a particular function.

Obviously the cells must be connected in someway AND there may be different types of cell cooperating with each other.

Examples of tissues

(a) Epithelial tissue

Layers of epithelial cells make up epithelial tissue which covers a lot of the body, including the inside of the gut, including the stomach.

(b) Muscle tissue

muscle tissue

Muscular tissue must have the ability to contract (and relax) to move whatever the tissue is attached to e.g. bones.


(c) Glandular tissue

Glandular tissues are production sites for enzymes and hormones - important secretions for the efficient functioning of organs.

3. Examples of organ and gland cells

An organ is a group of different specialised tissues that work together to perform specific functions.

Examples of organs

The stomach - part of the digestion system

The stomach is an organ that uses all of the three tissues mentioned above.

The inside and outside lining of the stomach is made from epithelial tissue - it holds the stomach together and contains food starting to be digested.

The wall of the stomach has attached muscle tissue to enable it to churn up food prior to digestion.

Glandular tissue makes digestive juices to breakdown the food at the start of the digestion process.

(Other examples of glandular tissue structures include the pituitary gland, the adrenal gland and the thyroid gland.)

4. From tissues and organs to organ systems

An organ system is a group of organs that work together to perform overall a more complex function - each organ performs its own function as part of the overall process

Examples of organ systems

The digestive system of mammals is an excellent example of an organ system - this organ system breaks down food and absorbs the molecules and ions.

It consists of a whole series of organs and glands working together.

(1) The pancreas and salivary glands produce digestive juices containing enzymes to break down food.

(2) The stomach and small intestine digest the food - nutrients pass from the small intestine to the blood stream - absorption of soluble food molecules.

(3) The liver produces bile that helps digestion in the small intestine.

(4) The large intestine absorbs water from undigested food to leave the waste as faeces.

See Enzymes - including structure and function of digestion system

Other organ systems in the human body (with links to detailed notes)

The human body contains 11 important organ systems, including:

circulatory transport system - blood vessels and heart (cardiovascular system),

respiratory system - from mouth to lungs

digestive (described above) - oesophagus, stomach, small intestine, large intestine and anus

excretory system - kidney, urinary bladder, ureter, urethra

nervous - central nervous system and brain (and specific brain notes)

endocrine systems - complex system of glands and small organs

skeletal and muscle systems

reproductive systems

A summary of human sense organs

All these systems work closely together to maintain a fully functioning healthy human body.

The failure of any of the organ systems can lead to a serious, and potential fatal, medical condition.

5. More summary examples as part of whole organism

e.g. part of an animal organism

epithelial cell ==> epithelial tissue ==> stomach organ lining ==> upper part of digestive organ system ==> full digestion system from mouth to anus

e.g part of a plant organism

palisade cell => palisade tissue => plus other tissues makes up a leaf => plus more leaves and other organs gives a plant

BUT remember, relatively large multicellular systems consist of multiple organ systems.

Summary of learning objectives and key words or phrases

  • Be able to describe cell organisation of plants animals in terms of from cells to tissues to organs to organ systems to whole organisms.
  • Know that the cells of multicellular organisms may differentiate and become adapted for specific functions - specialised cells.

  • Know that tissues are aggregations of similar cells and organs are aggregations of tissues performing specific physiological functions eg heart and liver.

  • Know that organs are organised into organ systems, which work together to form organisms.

  • Know that large multicellular organisms develop systems for exchanging materials.

    • Know that during the development of a multicellular organism, cells differentiate so that they can perform different functions.

    • The specialised cells form tissues, one or more types of tissue are structured to form organs and two or more organs can work together in an organ system.

    • Bigger multicellular systems e.g. animals like mammals have several different organ systems for absorbing (e.g. gut), transporting (e.g. blood system) and exchanging materials (e.g. lungs).

  • You should develop an understanding of size and scale in relation to cells, tissues, organs and organ systems.

  • Know that a tissue is a group of specialised cells with similar structure and carry out a particular function.

  • Know that examples of tissues include:

    • muscular tissue, which can contract to bring about movement eg contraction and relaxation to move limbs

    • glandular tissue, which can produce and secrete substances such as enzymes to enable chemical reactions and hormones to control certain functional features of an organism,

    • epithelial tissue, which covers some parts of the body including the inside of the gut and the skin.



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General HUMAN BIOLOGY revision notes

See also cell biology section

Introduction to the organisation of cells => tissues => organs => organ systems

Homeostasis - introduction to how it functions (negative feedback systems explained)

Homeostasis - control of blood sugar level - insulin and diabetes

Homeostasis - osmoregulation, ADH, water control, urea/ion concentrations, kidney function, dialysis

Homeostasis - thermoregulation, control of temperature

The brain - what the different parts do and the dangers if damaged

An introduction to the nervous system including the reflex arc

Hormone Systems - menstrual cycle

Respiration - aerobic and anaerobic in plants and animals.

Keeping Healthy - Diet and Exercise

Keeping Healthy - How do our bodies defend themselves against infectious diseases? 

See also Enzymes - section on digestion and synthesis

Examples of surfaces for the exchange of substances in animal organisms

Optics - lens types (convex, concave, uses), experiments, ray diagrams, correction of eye defects (gcse physics)

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