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Doc Brown's Biology AQA GCSE Additional Science-BIOLOGY 2 Revision Notes

Biology Unit B2.2 Tissues, organs and organ systems Study Notes

BIOLOGY UNIT 2 Biology 2 for GCSE Additional Science or GCSE Biology

REVISION NOTES GUIDE SUMMARY: What do you need to know for the examinations? What do you need to able to do in the exams? In AQA GCSE Science A examinations HT means for higher tier students only. Sorry, but I don't have much time to answer questions, but if you see any apparent errors or wish to comment, please email me. All my notes, learning objectives, comments for exam revision are based on the official AQA GCSE Science A Key Stage 4 syllabus specification.

  • AQA GCSE Science BIOLOGY 2 Unit B2.2 Tissues, organs and organ systems

    • 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.


    AQA GCSE Science BIOLOGY Unit B2.2.1 Animal organs

    • a) 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.

    • b) 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.

    • c) Know that organs are made of different tissues acting together to perform some particular function.

      • Know that one organ may contain several tissues.

      • Know that the stomach is an organ that contains:

        • muscular tissue, to churn the contents and break up the food into smaller chunks to aid digestion,

        • glandular tissue, to produce digestive juices containing enzymes to break food down at the molecular level,

        • epithelial tissue, to cover the outside and the inside of the stomach.

    • d) Know that organ systems are groups of organs that work together to perform a particular function.

      • Know that the digestive system is one example of a system in which humans and other mammals exchange substances with the environment.

        • The digestion process requires a variety of enzymes to breakdown food into soluble products we can absorb from the digestive system, and these enzymes are produced by specialised cells in the glands and gut system.

        • Large insoluble molecules like proteins, starch like carbohydrates and oils/fats cannot pass through the membranes of the cell walls of the gut system.

        • However, smaller soluble molecules like amino acids, sugars and fatty acids can pass through the walls of the digestive system.

        • Some examples of the enzymes responsible for the breakdown of large insoluble molecules into small soluble absorbable molecules are ...

          • protease enzymes like pepsin convert proteins to amino acids,

          • carbohydrase enzymes like amylase convert carbohydrates like starch to sugars,

          • lipase enzymes convert oils/fats to fatty acids and glycerol

      • Know that the digestive system includes:

        • (1) In the mouth, salivary glands produce the enzyme amylase which can break down carbohydrates like starch. The saliva also moistens the food and, together with the chewing action (mastication) of the mouth muscles, balls of food are formed that are easily swallowed.

        • (2) The oesophagus (gullet) is a tube that connects the mouth to the stomach and its lined with muscles that help move the balls of food along (this action is an example of peristalsis).

        • (3) In the stomach the food is churned and broken up into smaller chunks by the muscles of the stomach wall. The protease enzyme pepsin is secreted which can break down proteins to amino acids. At the same time hydrochloric acid is produced, killing most of the bacteria present and creates the right acidic pH conditions (~pH 2) for the protease enzyme, which works best in these acid conditions to break down proteins.

        • (4) The liver produces alkaline bile, which neutralises excess stomach acid (most enzymes can't work in very acid conditions), and bile helps to emulsify oils/fats. The emulsification is essential for the efficient faster digestion of oils/fats, the oils/fats are more dispersed giving greater surface area (greater surface area - think of the oil/fat as broken down into smaller droplets/particles).

        • (5) The gall bladder stores bile before its released into the small intestine to help with digestion.

        • (6) The pancreas gland produces digestive juices containing the enzymes (i) protease pepsin (breaks down proteins), (ii) amylase (breaks down starches) and (iii) lipase (breaks down oils/fats), which are released into the small intestine.

        • (7) The small intestine is where digestion process continues with the release of the enzymes from the pancreas. Here the absorption of soluble food into the blood stream occurs from the digestive system eg smaller molecules like amino acids, sugars and fatty acids - the products of enzyme breakdown of larger food molecules (x-reference with the enzymes above, which are released into the small intestine).

        • (8) In the large intestine excess water is absorbed from the undigested food, producing faeces which are initially stored in the rectum before release through the anus!

      • You should be able to recognise the organs of the digestive system on a diagram and know their function where described in this module (Biology B2).

        • eg salivary glands, stomach, gall bladder, liver, large intestine, pancreas, small intestine, rectum

        • The functions of the components of the digestion system are described in the section above.


    AQA GCSE Science BIOLOGY Unit B2.2.2 Plant organs

    • a) You should know that plant organs include stems, roots and leaves.

      • Details of the internal structure are only needed for the leaf.

      • Know the structure and function of palisade cells and guard cells in plants.

      • Palisade cells contain chlorophyll and are adapted for photosynthesis.

      • Guard cells are adapted to open and close the pores which allow gas exchange and water evaporation.

    • b) You should know examples of plant tissues including:

      • epidermal tissues, the outer layers which cover the whole plant,

      • mesophyll, between two epidermis layers, where most photosynthesis happens,

      • xylem and phloem, which transport substances around the plant eg sugars like sucrose and glucose, minerals and water.

    AQA GCSE Additional Science BIOLOGY

  • When revising, these pages provide you with a summary of what you need to know and be able to do.

  • BUT remember, your primary source of revision are your class notes, investigations and AQA GCSE science textbooks.

  • AQA GCSE Additional Science AQA GCSE Biology Unit B2 Index:

  • **

  • Website content copyright Dr W P Brown 2000-2013 All rights reserved on revision notes, puzzles, quizzes, worksheets, x-words, images etc. Copying of website material is not permitted


keywords:  multicellular organisms differentiated cells adapted specific functions tissues muscular glandular enzymes hormones epithelial tissue digestive system stomach small/large intestine liver bile epidermal mesophyll tissue xylem phloem


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