• 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. 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. 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
  7. 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
  8. 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
  9. 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
  10. 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
  11. 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

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.