Biology B2


Biology B2

Contents:

B2.1 Cells and simple cell transport
B2.2 Tissues, organs and organ systems
B2.3 Photosynthesis
B2.4 Organisms in their environment
B2.5 Proteins and enzymes
B2.6 Aerobic and anaerobic respiration
B2.7 Cell division and inheritance

B2.8 Speciation

This is a preview of the Biology B2 syllabus. This page is designed to show you what GCSE Revision 101 can offer you if you buy the revision app, available for iPad. The link to purchase the app, for only £1.49 are below. Each module includes the syllabus straight from AQA, full revision notes written by myself including exclusive diagrams, interactive quizzes, key summarised points, end of unit questions, and exam-style questions.

To access units B2.2 to B2.8, buy the app and you’ll have all the notes below and more for each unit!

Buy access to the online textbook (all Sciences for only £5): 

Buy the app from the iTunes Store:   

B2.1 Cells and simple cell transport

AQA Syllabus content:

  • Most human and animal cells have:
    • a nucleus which controls the activities of the cell
    • cytoplasm, in which most of the chemical reactions take place
    • a cell membrane, which controls the passage of molecules into and out of the cell
    • mitochondria, which is where most energy is released in respiration
    • ribosomes, which is where protein synthesis occurs
  • Plant and algal cells have a cell wall made of cellulose, which strengthens the plant. Plant cells also have:
    • chloroplasts, which absorb light energy to make food substances
    • a permanent vacuole filled with sap
  • A bacterial cell contains cytoplasm and a cell membrane surrounded by a cell wall. The bacterial chromosome is not contained in a distinct nucleus
  • A yeast is a single-celled fungal organism which has cytoplasm, a nucleus and a cell membrane surrounded by a cell wall
  • Cells may be specialised to carry out a particular function
  • Dissolved substances can move into and out of cells by diffusion
  • Diffusion is the spreading of the particles of a gas, or of any substance in solution, resulting in a net movement from a region where they are of a higher concentration to a region with a lower concentration. The greater the difference in concentration, the faster the rate of diffusion
  • Oxygen required for respiration passes through cell membranes by diffusion

Animal cells
An animal is a multicellular organism composed of anything from thousands to billions of cells. There are very simple animals such as jellyfish, and then there are very complex animals such as humans, which are made up of many different types of specialised cell which have specific purposes. The interesting thing about animal cells is that they are very similar to most living cells in terms of the things they contain. We call these things organelles, and some of the most important ones in animals are:

  • the nucleus is the informational body of the cell which contains all of the cell’s genetic material (DNA). The nucleus is the site of the cell where most of its activities are regulated, and where the instructions come from to make new proteins and other cells
  • the cell membrane (or the plasma membrane) is a thin layer composed mainly of fat which encases the cell. The cell membrane protects the cell from damage, stops the cell contents mixing with the outer environment and controls the passage of materials from outside the cell to the inside
  • the ribosomes are tiny organelles dotted all around the cell which are responsible for producing proteins. They receive information from the nucleus which is translated into instructions for making a new protein. Ribosomes make all cell proteins
  • the mitochondria are often called the ‘molecular powerhouses’ because they are the site of aerobic respiration, where most of the cell’s energy is released. Inside a mitochondrion is where oxygen from respiration is used to release energy for the cell’s needs
  • the cytoplasm is a liquid jelly-like solution in which all of the other organelles are found in. Most chemical reactions in the cell take place in the cytoplasm

Plant cells
Plants are also multicellular organisms – but they behave in very different ways. They are said to be sessile, meaning they are fixed to one point, since they cannot move about like animals. They are also photosynthetic meaning they make their own food in a process called photosynthesis. Plants cells are quite similar to algal cells (algae are much more primitive aquatic organisms which the plants evolved from). Both plant and algal cells contain all of the features of animal cells outlined above as well as a cell wall. The cell wall surrounds the cell membrane and provides extra support and protection. Pressures inside animal cells can be very high, which is why the cell wall protects them from bursting when the cell expands due to movement of water into and out of the cell. The cell wall is made from a carbohydrate molecule called cellulose.

1        Why do plant and algal cells have a cellulose cell wall?

In addition to all these features, many plant cells also have a vacuole, which is filled with cell sap and is important for molecular storage and keeping the plant cell rigid for support. The vacuole also serves to store many of the plant cell’s waste products or molecules which might be toxic to other parts of the cell (keeping toxic molecules out of the cytoplasm).

The other really important organelle found in plant cells (and also the cells of green algae) is the chloroplast, which is where photosynthesis takes place. Chloroplasts are filled with photosynthetic pigments called chlorophylls which are what make photosynthetic tissues (such as leaves) green.

2       Plant cells are highly-differentiated, for example root cells do not have any chloroplasts whereas leaf tissue cells have thousands of chloroplasts. Why might this be?

Bacterial cells
The number of different species of bacteria on our planet is huge. Bacteria are very different from animal or plant cells because they are said to have ‘no true nucleus’ – meaning their DNA is not contained within a nucleus – instead they have one long loop of DNA called the circular chromosome floating in the cytoplasm. Many bacterial cells also have plasmids, which are separate small loops of DNA which can be exchanged between bacteria.

Bacterial cells are really tiny compared to animal or plant cells. They are in length usually less than 1 µm (one micrometre, which is one thousandth of a millimetre!), and are covered in a cell wall, which is very different from the plant or algal cell wall. The wall may be encased by a slime capsule, and may have flagella attached (singular: flagellum), which are tail-like structures which bacterial cells whip back and forth to proper themselves around.

3        What is different about the bacterial chromosome compared to human DNA?

Yeast cells
Much like bacteria, yeasts are single-celled organisms. They belong to the fungi kingdom, and like animal and plant cells they contain a nucleus which houses the genetic material. Yeast cells are filled with fluid cytoplasm containing mitochondria and ribosomes, and are enclosed by a cell membrane and an outer cell wall, again different to the cell walls of bacteria and plants, fungal cell walls are composed of the molecule chitin. The whole cell is much larger than a bacterial cell, ranging from about 3 µm to about 4 µm in length. Yeasts may also contain a vacuole which is filled with water and used for storage and support.

Yeasts reproduce by a method known as asexual budding. This occurs when a new cell buds out from an existing cell, resulting in two new cells when they split in half. During this process, all the organelles (mitochondria, ribosomes) and the yeast DNA are copied so that each new cell will be identical.

When yeasts do not have access to lots of oxygen, they can respire anaerobically. This is very different from our method of anaerobic respiration, as with yeasts, rather than producing lactate, ethanol is produced along with carbon dioxide. This process which produces ethanol is called fermentation.

4        Why do brewers of beers use yeast in the production process?

5        Can you name any other uses of yeasts?

Specialised cells
Looking at any cell in the human body, you immediately notice how its properties make it very good at doing what it does. This is because many cells are specialised, meaning they have specific features which make them better suited at performing a specific task. This is not just true for humans – most multicellular organisms such as animals and plants have many different types of cell, specialised for particular functions. We can look at the structure and contents of cells to give an idea of what that cell is needed for.

Below are some of the adaptations of cells from animals. It is important to understand how these adaptations help a cell at its specific function.

A sperm cell (also called a spermatozoon) needs to fertilise an egg to produce an embryo. Its headpiece contains an acrosome which releases digestive enzymes to break down and penetrate the lining of the egg, as well as a large, condensed nucleus. The midpiece is packed full of many mitochondria to supply the sperm with energy for movement, which is achieved by the flicking of the tail, which allows the cell to swim towards the egg

Red blood cells (or erythrocytes) have a thin outer membrane and lots of oxygen acceptors, making oxygen uptake more efficient. They are also shaped like biconcave discs to increase their surface area for more diffusion of oxygen. Red blood cells also do not have a nucleus at all, which gives more room for packing haemoglobin, the oxygen-carrying proteins inside red blood cells

Fat cells act as food reserves and help to insulate, and are made when energy intake exceeds energy use. They are very large but have only a small amount of cytoplasm, making a lot of room for fat stores. They are expandable because they have a loose membrane and cytoskeleton which support cell expansion as it fills up with fat. There are also relatively few mitochondria and ribosomes as they do not need many proteins or much energy

The main cells of the eye are cone cells (to see colour) and rod cells (night vision). Cone cells have multiple synapses which send information to the optic nerve. They also are packed full of mitochondria as they need a lot of energy in the process of converting visual pigment from one form to another in response to light detection. Having a lot of energy released by many mitochondria allows us to constantly see in colour

Diffusion
The red blood cells is an example of a cell that is well-adapted for transport of molecules around the body – it carries oxygen around the bloodstream that is picked up by its haemoglobin proteins. But how does the oxygen get into the red blood cell? There must be a mechanism by which molecules move into and out of cells. One of the simplest ways in which molecules can move over a membrane is through diffusion.

Diffusion is the net movement of dissolved substances (solutes) or gas particles from an area of higher concentration to an area of lower concentration.

In a solution, various molecules all move around in a random motion – there is no direction. It is only because of the random movement of the particles that there is a net movement from areas of higher concentration to areas of lower concentration, because random movement results in more particles (on average) moving down the concentration gradient than moving against it.

The concentration gradient is described as the difference in concentration of a solute between two regions. The greater the concentration gradient between two areas, the faster the rate of diffusion will be because there will be more random net movement of particles from high concentration to low concentration.

The rate of diffusion from one area to another is also affected by temperature. Raising the temperature will increase diffusion rate because it causes particles to move more quickly down the gradient.

When describing the movement of molecules down the concentration gradient it is important to understand that when talking about diffusion, the net movement is always down the concentration gradient – not up the gradient.

Diffusion can happen over a cell membrane because membranes are described as being semi-permeable, meaning it will allow some molecules to diffuse across it. This is how molecules get into and out of cells. One example of this in the human body is seen in the uptake of oxygen by red blood cells in the lungs.

6        Suggest, by looking at the diagram, how the alveolus (tiny air sac in the lung where gaseous exchange takes place) membrane is adapted for exchange of gases to red blood cells

Many cells are adapted specifically to increase rates of diffusion. This is most often achieved by folding the cell membrane in order to increase the surface area of the cell surface, so that more molecules can diffuse over the membrane down the gradient. Such foldings are called microvilli (singular: microvillus).

This is a preview of the Biology B2 syllabus. This page is designed to show you what GCSE Revision 101 can offer you if you buy the revision app, available for iPad. The link to purchase the app, for only £1.49 are below. Each module includes the syllabus straight from AQA, full revision notes written by myself including exclusive diagrams, interactive quizzes, key summarised points, end of unit questions, and exam-style questions.

To access units B2.2 to B2.8, buy the app and you’ll have all the notes below and more for each unit!

Buy access to the online textbook (all Sciences for only £5): 

Buy the app from the iTunes Store:   

96 thoughts on “Biology B2

  1. Hello.

    Firstly, I would like to thank you for this valuable resource you have provided me and everyone else. This really helped me during my exam. I am currently doing a coursework in C3 extension GCSE and having a look at the C3 downloadable sheet, I can now take some notes from there. Thank you.

    Would you be kind enough to make P2, C2 and B2 available in pdf?

    Thank you.

  2. I love this website guys! 🙂
    It helped to revise lots and lots.
    With the help of this page i managed to just scrape an F grade.. which im really proud of 🙂
    Thanks again guys.

  3. thankyou this has been very helpful, i was just wondering are there any answers for the little questions at the end of the notes? thanks xx

  4. i love this website it’s soooo coooool (H)
    I LOVE SCIENCE
    its my favourite subject and i love the teacher!
    thank you for all the help:D

  5. dear webiste 🙂
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    you are in my favourites and i will gaze at you every night before i go to sleep!
    THANK YOU SO MUCH I LOVE YOU

  6. dear webiste 🙂
    you are the most useful, special thing in the world 🙂
    you are in my favourites and i will gaze at you every night before i go to sleep!
    THANK YOU SO MUCH I LOVE YOU LOTS

    • hahah That’s exactly what i’ve been thinking!! 😀 if only i knew about in Y10, i could have started revising early!

  7. Pingback: Thanks to all who use GCSE Revision 101. Here’s a summary of how we did this year! « GCSE Revision 101

  8. This sites helped me alot. thankyou do much!
    just wondering if you could maybe put up some revision material for c1a, c1b, b1a, b1b, p1a, p1b … ?
    would really help alot!
    THANKS! please consider it!

  9. Thank you, Thank you, Thank you!
    i owe it all to you!
    i got 98%-a* my Chemistry 2 and 88%-a on this exam (b2)
    THANK YOU!
    xxxxxxxxxxxxx

  10. this website is amazing !! thank you soo much, it’s soo usefull !! im doing b1, b2 and c2 retakes and having to find worksheets in my folder is awfull as so many things are missing :S this completes all my revision. THANKS I owe my life to you !!

  11. this website is great! but .. would be better if B1 B2 and B3 werent mixed up. im learning B2 and half the stuff on this page is not what i am learning. need a page for each different topic to make it clearer !

  12. Hey,

    Absolutely fantastic website- one thing I spotted you’ve missed was that bile not only increases the pH (neutralising stomach acid) but also acts as an emulsifier and increases surface area, which increases the rate that the ‘food’ can be digested at. It’s just one fact I always remember and I didn’t see it here!

    Otherwise- live saver of a website. I unfortunately do edexcel igcse physics which is a pain and means this isn’t my exact syllabus. I’ll still have a look through it though!

  13. um actually for limitng factors, water is NOT a limiting factor. just to let you know. don’t want you revising the wrong stuff

    • Although not classed as a limiting factor, at the time of writing these at least, the AQA-endorsed textbook suggested that ‘water availability’ be studied also as it does have an effect on plants. But yes, you’re right, it’s not a limiting factor.

  14. ^hmmm it would be awesome if there is an answer page for the B2 End of Unit Questions….but nevertheless this website is some good revision material…. :]

  15. what i would like to say that there is an erorr in this page where you have mentioned that Osmosis is the movement of water from an area of high concentration to an area of low concentration across a semi-permeable membrane. that is totally wrong,Hence the right explanation for your misundersanding is Osmosis is the movement of water from a less concentrated solution to a more concentrated solution through a partially permeable membrane.

    • Actually, you’ll find my definition is correct. When I say an area of high concentration, I do of course refer to a high concentration of water molecules. Your definition suggests a lower concentrated solution (as in less solute, more water) which is exactly the same thing. As for the ‘semi-permeable’ or ‘partially permeable’ membrane, yes, you’re right it is correct to call it a partially permeable membrane, but at GCSE level there shouldn’t be a penalty for naming it ‘semi-permeable’, only at A Level does this become important.

  16. Appreciate this guys! Keep the revision notes up its a great help to all of us and we wouldn’t have the grades we have today if it wasnt for you!

  17. These notes are amazing! They contain everything in my GCSE Additional Science (AQA) and I can download them into iBook with the PDF files so I can revise anywhere on my ipod!
    Thank you for making these they have helped so much. Told all my friends taking the same courses!

  18. hey quick question can animal cells be turgid or flacid or is it just plant cells a bit confused btw this website is amazing its the key to success 😀

    • Good question. Both animal and plant cells can be affected. You only need to know the terms ‘flaccid’ and ‘turgid’ but these notes come directly from my revision site for AS Biology if you want more information:

      The cell membrane is a partially permeable membrane. Placing plant or animal cells in pure water, or in any solution with a water potential higher than the cell contents, means there is a water potential gradient from outside to inside the cells. Water molecules will move down the water potential gradient into the cells by osmosis. The cells will swell. In the case of animal cells, the cell will eventually burst open – it is haemolysed. In a plant cell, the swelling vacuole and cytoplasm will push the membrane against the cell wall. It will not burst because the wall will eventually stop the cell getting any larger. Osmosis will then stop at this point, even if the concentration gradient remains. The cell is turgid. Placing animal or plant cells in a salt or sugar solution (with a water potential lower than the cell contents) means there is a water potential from insider to outside the cells, so water molecules move out of the cells by osmosis. The cells will shrink, and in the case of animal cells, the cell contents will shrink and the membrane will wrinkle up – the cell has crenated. With plant cells, the cytoplasm and vacuole will shrink as they lose water, the cell surface membrane will pull away from the cell wall – this is called plasmolysis.

  19. THANK YOU SOOOO MUCH. I’m rubbish at revising, but I can read through this page with no trouble rather than all the babbling in the text book. I did great in my mocks after reading B2 C2 and P2 (all A*s) and have real B” tomorrow, C2 on Thursday and P2 on Monday. So I’m rereading the site and all I can say is THANK YOU.

  20. Thank you for these references: P2, C2 and B2. It will save me time reading books and will definitely help me to supervise my son’s revision:-)) Keep up the good work and God bless!

  21. hey, how do i download the biology, chemistry and physics unit 2 courses?
    and thankyou so much, these are really helpfull

  22. hey, erm i commented quet abit ago, asking how i can download the biology, chemstry and physics unit 2 courses, if you could help me it would be very much appreciated.
    great websit by the way, very helpful!:)

  23. Tupac made this site, and therefore the illuminati will shut it down. Please switch owners and stop hiding tupac.

    • This is for the 2009-10 syllabus onwards. There have been subtle changes to the specification each year which is why these notes will eventually be outdated. As I am uni I cannot really be updating these though, which is why there is a disclaimer on the site about this fact. Most important thing to remember is that this shouldn’t be used as a sole revision tool or to get an idea as to what the syllabus/specification is, but should only supplement your revision. It just explains topics nicely and briefly. Hope this helps, D

  24. Hiya these notes would have helped with my biology exam yesterday, but my lovely friend (who has her birthday today) didnt know about it. i’ll make sure i give her a huge birthday KISS 🙂

  25. These would have helped with my biology exam yesterday, however my idiot friend Rodie didnt tell me about it. no worries she will be murdered asap =)

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