Edexcel IGCSE Biology Movement of substances into and out of cells

MOVEMENT OF SUBSTANCE IN AND OUT OF THE CELLS

ACTIVE TRANSPORT
  • Movement of particles from a region of low concentration to a region of high concentration.
  • Particles move against the concentration gradient.
  • It requires energy.
  • Cells involved in active transport should have lots of mitochondria
PASSIVE TRANSPORT
  • Movement of particles from the region of high concentration to a low concentration.
  • Particles move along the concentration gradient.
  • It does not require energy
  • Having numerous mitochondria is not a requirement

DIFFUSTON

OSMOSIS

DIFFUSION

  • It the net movement of particles from an area of higher concentration to an area of lower concentration.
  • It is passive process
  • It happens along the concentration gradient
  • No use of energy.

FACTORS AFFECTING DIFFUSION

SURFACE AREA

  • Greater the surface area greater is the rate of diffusion as particle will get more room for movement.
  • All the exchange surfaces have greater surface area like root cells has root hairs and intestine cells has villi.

CONCENTRATION GRADIENT

  • Greater the difference in concentration in the two region greater is the rate of diffusion.
  • All the exchange surfaces maintain steepest concentration gradient
  • Like root cells are closed to xylem and Villi has rich blood supply.

DIFFUSION DISTANCE

  • Smaller the diffusion distance greater is the rate of diffusion as the particles have to travel a smaller distance.
  • All the exchange surfaces maintain a smaller diffusion distance by being one cell thick.

TEMPERATURE

  • Greater the temperature greater is the rate of diffusion as particles will get more kinetic energy for movement
  • Rate of Diffusion = Surface area x Concentration gradient/Diffusion Distance

OSMOSIS – Special Case of Diffusion

Osmosis is the net movement of water particles from the region of high concentration of water particles to low concentration of water particles across a semi permeable membrane.

Movement of water from a dilute solution to a concentrated solution through a semi permeable membrane.

Special Case:

  • It is the diffusion of only water molecules
  • It required a semi permeable or partially membrane
  • Membrane that allows only specific molecules to pass through like water.

OSMOSIS IN PLANTS

  • Hypertonic – The outer solution has a less concentration of water than inside the cell.
  • Isotonic – The outer solution has same concentration of water than inside the cell.
  • Hypotonic – The outer solution has a greater concentration of water than inside the cell.

Plasmolyzed – The water moves out of the cells due to osmosis due to higher concentration of water inside the cell than outside. The cell membrane recetes from the cell wall

Flaccid – There will no net water movement so no pressure on the cell. It will be flaccid

Turgid – The water moves into the cell due to osmosis due to higher concentration of water outside the cell. The water will create pressure called turgor pressure on the cell wall making cell rigid and turgid.

Osmosis in Animals

ACTIVE TRANSPORT

  • Movement of substances from the region of low concentration to a region of higher concentration with the use of energy.
  • Dependent on respiration as it requires energy. So the cells involved in active transport has lots of mitochondria.
  • In Plants water and minerals are absorbed by active transport to absorb maximum of water and minerals.
  • In animals, the digested food gets absorbed into the blood by active transport to ensure maximum absorption
  • Salt glands are present in some marine organisms which removes the salt by active transport.

CELL CYCLE

Interphase –
  • It is the longest phase of the cell cycle
  • The cell grows in size and prepares all the proteins and enzymes needed for division.
  • Replication of DNA where DNA duplicates its content.
Mitosis
  • It is the division of the nucleus in which parent cell splits into two daughter nuclei containing same number of chromsomes as the parent cell.
Cytokinesis
  • It is the division of the cytoplasm which .takes place after the division of the nucleus.
Mitosis
  • It is the type of cell division in which a parent nucleus divides to form two daughter nuclei with exactly the same number of chromomes as that of the parent nucleus.
  • The daughter cells produced are genetically identical to the parent and are clones.
  • This division is important for growth, regneration and repair.
  • Mitosis is also important in asexual reproduction.

CELL DIFFERENTIATION

  • It is the process by which cell becomes specialised to perform a specific function.
  • Male Parent (23 pairs of chromosomes)                            Meiosis

Sperm (male gamete)

  • Female Parent (23 pairs of chromosomes) Meiosis

Ovum (Female gamete)

 

Animal Differentiation
  • In animals majority of the cells are differentiated at an early stage and different cells have specific functions like nerve cell, muscle cells.
  • Adult stem cells replaced the old and worn out cells in human but adult stem cells have limited specialization power
  • Majority of the differentiation is permanent
Plant Differentiation
  • Plants are the storehouse of stem cells
  • Root meristems and shoot meristems are the parts of actively growing part of the cells which contains stem cells.
  • The plants can be cloned easily as it has many undifferentiate cells and differentiation is not permanent.

STEM CELLS

  • Undifferentiate mass of cells that can differentiate into any cell type are known as stem cells.
  • Sources of Stem Cells : Embryo, left over remains of the embryo and the umbilical chord are the sources of embryonic stem cells.
  • Bone marrow is the source of adult stem cells.
  • Can solve the rejection problem if the transplanted organ is made from the person’s own stem cells.
  • Can be possible cure of neuro-degenerative diseases
  • Can be the potential cure of diabetes.
  • Therapeutic cloning.
  • Organ damage problem
ISSUES AGAINST STEM CELLS
  • It can lead to cancer as the stem cells are rapidly dividing.
  • The stem cells can be contaminated and can cause unwanted diseases to the patient.
  • Research is still slow and expensive
  • Research happens on aborted embryos which is considered as a potential source of life and many religions have ethical concerns against it.
  • The knowledge of the genes switched on and off using differentiation is still incomplete.

DISCLAIMER

Disclaimer: I have tried by level best to provide the answers and video explanations to the best of my knowledge. All the answers and notes are written by me and if there is any similarity in the content then it is purely coincidental. But this is not an alternative to the textbook. You should cover the specification or the textbook thoroughly. This is the quick revision to help you cover the gist of everything. In case you spot any errors then do let us know and we will rectify it.

References:

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Wikipedia

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