• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

AS and A Level: Molecules & Cells

Browse by

Currently browsing by:

Meet our team of inspirational teachers

find out about the team

Get help from 80+ teachers and hundreds of thousands of student written documents

  • Marked by Teachers essays 108
  • Peer Reviewed essays 26
  1. 1
  2. 2
  1. Marked by a teacher

    Relating the structure and function of cell organelles

    5 star(s)

    The inner membrane of nucleus will break down and allow chromosomes lying freely in cytoplasm. DNA contains the genetic information and control the synthesis of protein. Each cell contains millions of ribosomes. They are very tiny, non-membrane bounded organelles made of protein and RNA which consist of two sub-units that come together during protein synthesis. Ribosomes are distributed throughout the cell. Some of them are embedded in rough endoplasmic reticulum to translate a protein secreted into it while some flows freely in the cytoplasm for making protein that stays in the cell. Fused to the nuclear membrane is the endoplasmic reticulum.

    • Word count: 968
  2. Marked by a teacher

    The structure and function of the ileum in relation to absorption and digestion.

    4 star(s)

    * The lining epithelium is very thin and the fluids can pass rapidly through it. The outer membrane of each epithelial cell has microvilli which increase the exposed surface of the cell by 20 times. * There is a dense network of blood capillaries in each villus for quick absorption and maintainance of the concentration of the concentration gradient. * The villi possess smooth muscle fibres that contract and relax and mix the food up and bring it into contact with the epithelial cells of the absorptive surface. * Each villus has a lacteal for the absorption of fatty acids and glycerol, most of which combine to form fats.

    • Word count: 680
  3. Marked by a teacher

    My task is to describe how the cell structure of different cells is related to their function. I am going to carry out my task by researching different cells such as animal, plant, nerve cells etc.

    4 star(s)

    They function as an "antennae" of the neurone and are covered by thousands of synapses. These cells are linked to one another by electrical impulses and because of their long straight shape are able to transfer information around the nervous system quickly and uninterrupted. Red Blood cell Red blood cells perform the most important blood duty. A single drop of blood contains millions of red blood cells, which are constantly travelling through the body delivering oxygen and removing waste. If they weren't, everything in the body would slowly die.

    • Word count: 859
  4. Marked by a teacher

    Explain the link between cancer and mitosis. Describe how the chances of cancer developing in the human body may be increased.

    4 star(s)

    The problem is cased by mutations or abnormal activation of the genes which control cell division. We can say that a gene has been mutated if there is a change in one of the bases; for example, one base turns (e.g. adenine) into another base (e.g. thymine). This can lead to uncontrolled cell division. When genes are abnormal (or have been mutated) they are called oncogenes (onkos means tumour), about a hundred of which have been discovered. Cancerous cells will divide uncontrollably and repeatedly forming clones of genetically identical cells.

    • Word count: 726
  5. Marked by a teacher

    Cellular Respiration and the Role of Mitochondria

    4 star(s)

    The first stage, glycolysis is the anaerobic catabolism of glucose, it occurs in almost all cells. The process uses glucose and co-enzyme NAD (Nicotinamide Adenine Dinucleotide), and yields 2 molecules of Pyruvic acid, as below C6H12O6 + 2NAD+ -> 2C3H4O3 + 2NADH + 2H+ The free energy stored in 2 molecules of pyruvic acid is somewhat less than that in the original glucose molecule. Some of this difference is captured in 2 molecules of ATP. The Krebs Cycle then decarboxylates the pyruvic acid resulting in a 2-carbon fragment of acetate. This 2-carbon fragment is coupled to a molecule of oxaloacetic acid , this results in a molecule of citric acid (the process is also known as the citric acid cycle)

    • Word count: 750
  6. Marked by a teacher

    The aim of this activity is to investigate the effect of a reduction in enzyme concentration on the rate of reaction, in this case the breakdown of protein by protease enzymes.

    3 star(s)

    Risk Assessment: In this experiment there were not a lot of risk assessment that was dangerous to both my lab partner and I. The main risk assessments were to tie our hair back, we had to make sure that we didn't spill any of the chemical on the floor has this could be dangerous. Apparatus To carry out this experiment, the following apparatus are needed: * Trypsin * Milk powder * Standard laboratory glassware and apparatus * Stop clock * Colorimeter * Thermometer Reliability To be reliable, measurements should also be accurate.

    • Word count: 890
  7. Marked by a teacher

    Investigation to determine the effect of different brands of mouthwashes on microbes

    3 star(s)

    4 6.29 mm 4.79 mm 5.81 mm 1.90 mm 5 6.45 mm 4.42 mm 5.39 mm 2.64 mm Average 6.5975 mm 4.635 mm 5.3925 mm 2.074 mm Order of Zone of Clearance of Microbial Decay (Highest to Lowest) 1. Mouthwash A - Colgate Plax 2. Mouthwash C - Listerine 3. Mouthwash B - Dentyl Active 4. Mouthwash D - Superdrug Figures 1 to 3 show photographs of some of the results I collected from the pilot investigation. You can clearly see that different brands of mouthwash had different effects on the microbes as some destroyed them more than others and this is shown by a ring of clearance around each sample of mouthwash on the filter paper.

    • Word count: 765
  8. Marked by a teacher

    Observing Mitosis. The purpose of this experiment is to prepare a slide of actively dividing plant tissue and to observe stages of the cell cycle in living tissue.

    3 star(s)

    We put these roots into some acetic alcohol which is a fixative, so it stops and helps preserve the cells. Then we removed them and put them in ice cold water and then dried them on filter paper. After this we put the root tips in the pre-heated hydrochloric acid, this will dissolve the calcium pectate but leave the cell walls unharmed. So it breaks up tissue without damaging the cell.

    • Word count: 430
  9. Marked by a teacher

    Core practical(Why does the colour leak out of cooked beetroot?)

    3 star(s)

    * We took nine test tubes and labelled them from A-I. And we placed 6 cm3 of water in each tube with the help of pipette. * We put nine cylinders of beet root tissues into a beaker of 150 cm3 of water. * We put a beaker on a Bunsen burner and took some water and heated the water and then put a thermometer in to the beaker. * We put beet root in to the hot water for two minutes and noted the temperature.

    • Word count: 599
  10. Marked by a teacher

    Compare and contrast the structures/ultrastructures of cells

    3 star(s)

    In contrast to this, the similarities become evident only when the cells are looked at more closely. For example both plant and animal cells contain organelles, each one being assigned to a particular job. This is called 'division of labour'. This type of cell, where the nucleus is inside a nuclear envelope, and has other membrane-bound organelles, is called a eukaryotic cell.1There are new differences that can be discovered from using a more powerful microscope.

    • Word count: 549
  11. Marked by a teacher

    An investigation to determine how increasing the concentration of inhibitor Copper Sulpahte will affect the amount of juice pr

    3 star(s)

    This prevents enzyme substrate complexes formation, which means the enzyme can no longer function as it should. Therefore if i increase the concentration of the inhibitor it is more likely that the inhibitor will attach to an enzyme structure, meaning that a smaller ammount of enzymes are hydrolysing the same amount of pectin molecules, making less juice each time. Once the non-competitive inhibitor binds to the enzyme, it changes the shape of the active site, making the substrate unable to fit in its active site and therefore working properly. Enzymes: An enzyme is a protein that catalyzes or speeds up, a chemical reaction.They are biological catalysts.

    • Word count: 825
  12. Marked by a teacher

    The Advantages & Disadvantages of Using Enzymes in Medicine and Industry

    3 star(s)

    Non - competitive inhibitors change the globular shape of an enzyme so that a enzyme-substrate complexes can't form meaning a lower optimum rate of reaction. Enzymes in Medicine Enzymes can have good and bad effects to the body; it depends on the situation that they are being used in. For example some bacteria is a lot more dangerous than others because of certain enzymes that they contain, meaning that they can do things such as (depending on the enzyme) duplicate faster, inhibit other enzymes and break down substrate's that should not be broken down etc, in general cause more damage to its holder.

    • Word count: 895
  13. Marked by a teacher

    The use of pectinase in fruit juice production

    3 star(s)

    The pectin is broken down by enzymes in the pectinase group, which include polygalacturonases, pectin methyl esterase and pectin lyases. All three contribute to the breakdown of pectins from a variety of plant materials. Pectinase enzymes are produced during the ripening of some fruits and are also secreted by plant pathogens such as the fungus: Monilinia fructigena and the bacteria: Erwinia carotovora or the fungi: Aspergillus niger. The pectinase enzymes act in different ways on the pectins, for example they help soften their cell walls (they break down the cell walls).

    • Word count: 688
  14. Marked by a teacher

    How long does it take for the action of the enzyme 'amylase' (a type of carbohydrate) to break down the carbohydrate 'starch'?

    3 star(s)

    Factor to be investigated: The temperature factor will be investigated. This will indicate whether by increasing the temp, or decreasing the temp, will have any effect on the speed at which the starch is broken down by the enzyme. Prediction It is expected that as the temperature increases, starch molecules will be broken down more quickly. However, the temp may reach a point the enzyme de-natures, or stops working. This can be expected to be above 37.5�C. (At this temp enzymes and other biological materials may become damaged/ destroyed). The activation site may become wobble-like, and unusable, so stopping starch molecules from being broken up (see diagram).

    • Word count: 659
  15. Marked by a teacher

    How Does Temperature Affect the Action of Amylase on Starch?

    3 star(s)

    When the amylase is heated too much, it will stop the amylase molecules working because they will die. The optimum temperature for enzymes is about 37�C because this is body temperature, and this will produce the best results. Variables: * Temperature - The changed will be changed during this experiment. I will be changing the temperature at 5�C intervals starting at 20�C. * Time - The time taken to break to break the starch down according to the temperature will be recorded. Method: 1) The spotting tile will have the different temperatures of the amylase written on.

    • Word count: 591
  16. Marked by a teacher

    The Effect Of pH On Invertase Activity.

    3 star(s)

    Furthermore, there is a most favorable pH for enzyme - the point where the enzyme is most active. This point is known as the optimal pH. The aim of this experiment is to find out the range of pH which invertase is effective. Method This experiment was based on the premise that activity of invertase will be affected by different pH. Benedict solution was used as an indicator to determine whether the invertase had been denatured or not. If invertase was not denatured, glucose and fructose were produced. Benedict solution then would react with glucose and change its colour from blue to red.

    • Word count: 852
  17. Peer reviewed

    The effect of drugs on the nervous system

    5 star(s)

    The PNS receives thousands of sensory inputs and transmits them to the brain via the spinal cord. The brain will then process this information, discarding around 99% of it as unimportant. After this sensory information has been processed, areas of the nervous system generate nerve impulses to organs or tissue and form a suitable response. As influences from chemicals are able to affect how the nervous system functions, it can be assumed that chemicals such as drugs are potentially able to change the way an organism functions. Whilst our knowledge of different regions of brain function and neurotransmitters within the brain is limited, explanations involving the mechanisms of drugs may be vague.

    • Word count: 923
  18. Peer reviewed

    The Function and Structure of Lipids in Living Organisms

    4 star(s)

    Fatty acids can be saturated or unsaturated depending on their carbon bonding and can be told apart easily because of their state at room temperature, ether solid or liquid. Saturated fatty acids are made up of hydrogen, oxygen and carbon, the carbon in the saturated fatty acid has single bonds and it is bonded to the maximum number of atoms that it can bond with. Because of this it is a strait chain which means that it can be closely packed with other chains which means that it is a solid at room temperature.

    • Word count: 977
  19. Peer reviewed

    Skeletal System. What is the difference between the axial and appendicular skeleton? What is the difference between ligaments and tendons? How are bones important in maintaining homeostasis?

    4 star(s)

    The human endoskeleton skeleton is a combination of cartilage and 206 bones that make up the skeletal system. It is organized into two basic units: the axial skeleton and the appendicular skeleton. The axial skeleton supports the axis or trunk of the body and includes the skull, enclosing and protecting the brain, vertebrae of the spinal column, enclosing the spinal cord and the rib cage, around the heart and lungs. It includes 80 bones.

    • Word count: 428
  20. Peer reviewed

    Cell Structure

    4 star(s)

    * Contains molecules for the light dependant stage of photosynthesis * Synthesis of ATP * Enzymes required for conversion of CO2 and water to carbohydrate * Temporary storage of carbohydrate Sacs called thylakoids formed by membranes Stroma contains enzymes plants, protists (rare kleptoplastic organisms)

    • Word count: 536
  21. Peer reviewed

    Explain how the structure of collagen and haemoglobin are related to their function.

    4 star(s)

    Furthermore, the triple helix is held together by an extensive network of hydrogen bonds. Covalent cross-links are also present within tropocollagen molecules to impart the collagen fibre with strength and rigidity. Proline with its ring structure also helps in stabilizing the rigid three-stranded collagen helix. Beside, the tropocollagen molecules are arranged in a staggered manner with each other. This confers collagen greater strength. Secondly, it is insoluble in water. This is due to the large molecular size of the tropocollagen molecule and the nature of the amino acid residues. Each of the three polypeptide chains in a collagen molecule is about 1000 amino acid residues long and they coil up into a collagen helix.

    • Word count: 612
  22. Peer reviewed

    structural differences between fibrous and globular proteins.

    4 star(s)

    (X is proline, Y is either hydroxyproline or hydroxylysine) A globular protein has a more compact structure owing to highly contorted pattern of folding, bending and twisting along polypeptide chain to give the protein a spherical 3D shape while a fibrous protein is usually formed with elongated polypeptide chains wrapped around to form multi-molecular paralleled filaments to strands. For example, haemoglobin is a tetramer made up of 4 polypeptide chains of 2?

    • Word count: 398
  23. Peer reviewed

    The Biological Importance of Water

    3 star(s)

    This results in a hydrogen or H-bond, although technically speaking it is not actually a bond, just an attraction. As these molecules move around, the H-bonds continuously break and reform with other molecules. Although individually, these bonds are weak, the collective action of breaking and reforming means that together, the force is very strong.

    • Word count: 446
  24. Peer reviewed

    Objectives/Aims To measure and compare the amount of Vitamin C in various juices. To determine the effect of various factors on Vitamin C

    3 star(s)

    Pour 15ml of vitamin c indicator into 50 ml conical flask 2. Using clean pipette (Clean by rinsing in dist water), add a drop of one of the orange juice samples to the conical flask with indicator present. Gently swirly to mix the solution 3. Continue to add the sample of juice to the flask drop by drop, until the indicator changes from blue to colourless. NOTE: SWIRL AFTER EACH DROP ADDED: 4. Observe and count the number of drops of orange juice you needed to add to the conical flask to cause the indicator to lose all of it original colour.

    • Word count: 658
  25. Peer reviewed

    Describe the functions of the main cells components

    3 star(s)

    Diagram of a typical animal cell (3.bp.blogspot.com) The cell membrane (or plasma) is a thin skin around the cell. It gives the cell its shape and controls what goes into and out of the cell. If the plasma membrane was to get damaged in any way, and it wouldn't let anything enter or exit it, then we would not be able to get oxygen in and let carbon dioxide out. This means that we wouldn't be able to live, as we have to need oxygen and to let out carbon dioxide for respiration which provides our body with the energy to go through the processes that it needs.

    • Word count: 608

Marked by a teacher

This document has been marked by one of our great teachers. You can read the full teachers notes when you download the document.

Peer reviewed

This document has been reviewed by one of our specialist student essay reviewing squad. Read the full review on the document page.

Peer reviewed

This document has been reviewed by one of our specialist student document reviewing squad. Read the full review under the document preview on this page.