Biology AS Unit 1

Biology Unit 1

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  • Created by: Angelina
  • Created on: 29-03-13 14:34

Cell Terms

Stem Cell: Undifferentiated cells that can become a number of different cell typles. Found in bone marrow, umbilical cord, meristem and cambium.

Mitosis: Asexual reproduction, nuclear division that creates genetically identical cells.(Interphase), Prophase, Metaphase, Anaphase, Telophase.

Budding: How yeast cells reproduce.

Homologous Chromosomes: Have the same genes at the same loci, one from M and one from F.

Cytokinesis: Division of the cytoplasm.

Diploid: A cell with chromosomes in pairs.

Haploid: A cell with single chromosomes.

Cell signalling: How cells communicate with one another.

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Methods of Transport via cells

Osmosis: Passive net movement of water from a high solute concentration to a low solute concentration across a semi permeable membrane.

Diffusion: Net movement of molecules from a high to a low concentration, down a concentration gradient.

Transpiration: The loss of water vapour from the aerial parts of a plant due to evaporation.

Translocation: Is the movement of dissolved substances. It requires energy.

Passive: Requires no energy, e.g diffusion is passive.

Exocytosis: Pushing something outside the cell with the membrane fusing with it. Endocytosis is the opposite.

Water Potential: Is the ability of water to leave a solution. Measured in kilo pascals KPA.

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Breathing Inspiration and Expiration


  • The intercostal muscles and diaphragm muscles contract.
  • This causes the ribcage to move upwards and outwards and the diaphragm to flatten increasing the volume of the thorax.
  • As the volume of the thorax increases the lung pressure decreases to below atmospheric pressure.
  • This causes air to flow into the lungs.
  • Inspiration is an active process - It requires energy.


  • The intercostal and diaphragm muscles relax.
  • The ribcage moves downwards and inwards and the diaphragm becomes curved again.
  • The thorax volume decreases, causing the air pressure to increase above atmospheric pressure.
  • Air is forced out of the lungs.
  • Expiration is a passive process - It does not require energy
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Types of Circulatory Systems

Single Circulation:

  • Blood passes through the heart once as it completes a circuit of the body.
  • In fish it goes HEART-GILLS-BODY-HEART

Double Circulation:

  • Blood passes through the heart twice as it completes a circuit of the body.
  • In mammals it goes HEART-LUNGS-HEART-BODY-HEART

Open Circulation:

  • Blood flows from the heart, through the arteries to the body cavity. Oxygen is not transported by the bloos. Oxygen diffuses into the tracheal system. Found in Insects.

Closed Circulation:

  • Blood flows through blood vessesls. Found in humans and mammals.
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Structure Facts of the HEART

  • The muscle in the heart is cardiac muscle.
  • It is myogenic, contractions begin in the cells themselves.
  • Left side is thicker than the right side because that side pumps the blood further and at a higher pressure.
  • Semilunar valves keep blood flowing one direction to prevent backflow.

Atria at the top, Ventricles at the bottom

Sinoatrial node (SAN) is in the top right of the heart.

Atrioventricular node (AVN) is the middle of the heart above the ventricular septum.

Purkyne tissue is attatched to the AVN and it carries waves down the ventricular septum.

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Gas Exchange in Alveoli

  • Alveoli are arranged in bunches at the end of bronchioles.
  • They are surrounded by a network of capillaries, giving each alveolus its own blood supply.
  • Oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary endothelium.
  • Carbon dioxide diffuses into the alveoli from the blood crossing the capillary endothelium then the alveolar epithelium. After entering the alveolar space its breathed out.
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