HL 1 Biology

2.4b Active Transport

Percentages help: represent increase or decreases in relative terms and abolish the problem of variation between the samples used in experiments. Formula: (first number/second number)*100

Active Transportmovement of substances passing through the membrane with the use of energy (ATP). It is not diffusion. *ATP is the substance which supplies energy. All cells produces these supply of ATP by cell respiration. 

  • Active Transport can…
    • move substances against concentration gradient – from lower concentration to higher
    • make cells pump out substance, even if there is a larger concentration present outside (less common)
  • Examples using active transport…
    • plant roots absorb potassium + other ions
    • neurons pump potassium ions in and sodium ions out. Thus enables a creation of a store of potential energy/ electrical potential that will be used to transmit a nerve impulse

Cells consist many pump/transporter proteins which perform active transport, to control its cytoplasm. Each of these pumps have specific substances it will transport, thus cells can control what is absorbed and expelled. Work in a specific direction, too.

  • How it works: 
    1. Molecule or ioni enters the pump from the region with a lower concentration
    2. The particle then binds to a specific site.  (any other types of particles cant bind)
    3. Shape of the pump changes using energy from ATP
    4. Particle is able to pass to the other side of the membrane and the pump protein returns to its original conformation.

Vesicles are small fluid filled sacs usually inside the eukaryotic cells, made from a piece of the membrane. They work to move materials around the inside of cells. 

2 Main Processes to Transport Materials by Vesicles in the Cytoplasm:

  • Endocytosis: process when vesicles are formed at the inner surface of the plasma membrane of cells
    1. Using ATP, small part of the membrane is pulled in to form a vesicle
    2. As vesicle is pinched off, it traps fluid from outside the cell
    3. Vesicles are now able to move inside the cytoplasm, while carrying fluid inside.
  • Exocytosis: process of vesicles fusing with the membrane and expelling contents inside, out of the cell.
    1. Vesicles fuse with the plasma membrane
    2. Fluids inside vesicle are expelled
    3. Plasma membrane becomes flat again
  • *Exocytosis used to remove excess water from the cells of unicellular organisms, as well. 

Secretory cells are an example of vesicles moving materials around inside of cells.

  1. Protein is stored in the cisternae of the rER, after synthesized by ribosomes on the rER
  2. Vesicles that bud off from rER carry the protein to the Golgi apparatus
  3. Vesicles fuse with cisternae of Golgi apparatus to process proteins
  4. Golgi apparatus modifies the proteins
  5. Vesicles bud off from Golgi apparatus and carry processed proteins to the membrane
  6. These vesicles fuse with membrane, releasing proteins outside.

Plasma membrane separates the cell from the outside. Extracellular components are the structures outside the membrane. examples include:

  • The Plant Cell Wall
    • constructed by synthesized cellulose fibers in vesicles added to inner side of the cell wall
    • Maintains shape of cell
    • Prevents cell from bursting from high pressure
    • High pressure built inside the plant cells: prevents excessive water uptake by osmosis + makes cell very rigid/supports plant
  • Glycoproteins
    • Secrete of glycoproteins forms an extracellular matrix
    • Supports single layers of thin cells
    • Cell to cell adhesion
      • e.g. basement membrane help capillary wall cells and alveolus wall cells to adhere


Phosphate Absorption in Barley Roots (p. 35)

(1) Using the information from the table, it is apparent that the phosphate absorption level is decreasing as the oxygen concentration is reduced below 21.0%.  From the oxygen concentration of 21.0% to 2.1%, there is not much of an reduction in the phosphate absorption because its rate has fallen only by 0.01 from 0.33 to 0.32. Yet the oxygen concentration from 0.9~0.1 has shown a large reduction in the phosphate absorption.

(2) Reducing the oxygen percentage from 21.0 to 0.1 has a great reduction with the phosphate absorption. . In the cytoplasm of the root cells, the phosphate ions are assembled. Cells absorb these mineral phosphate ions through the process of active transport. During the process of active transport, energy/ATP supplied by cell respiration is necessary. When reducing the oxygen percentage, it would mean a reduction in the production of energy thus less absorption of phosphate.

(3) The roots absorbed the phosphate by active transport because there was a reduction in absorption of phosphate the more ATP was blocked by DNP concentration. With the increase in DNP the production of ATP by aerobic cell respiration will decrease, causing the membrane to not function and stop the process of active transport.

(4) From the data in the graph, we can conclude that the method of membrane transport used by the roots to absorb phosphate greatly rely on the process of active transport and production of ATP.

Autoradiography (p. 36)

1 (a) Rough endoplasmic reticulum

(b) In the rER, many amino acids are located at this area as protein synthesis occurs in this compartment.

(2)  Since the data shows a high % of autoradiographic grains are present in the vesicles after the 7 chase minute, we can deduce that the proteins are carried by vesicles from the rER to the Golgi apparatus. Followed by the vesicles, there is a high autoradiographic grain % in the Golgi apparatus which supports how the proteins has transferred to this organelle with the vesicles.

(3) Using the table, it would take about  117 minutes to synthesize and secrete protein from a pancreas cell. It would take just about 7 minutes for the protein to be synthesized and less than 117 minutes to transfer these protein throughout the cell.

(4) The limit on the amount of protein being released may have caused the amount of radioactivity in the duct adjacent to the cell not rising above 7.1%.  Because of this, the quantity of protein passing through will stop the amount of radioactivity to increase.

Chapter 2 Questions (p.37)

1 (a) I is the hydrophilic polar head and II are hydrophobic non-polar, fatty acid tails

(b) III  are integral proteins as for IV are the peripheral proteins. The integral proteins have less non-polar parts compared to the  peripheral proteins.

(c) V is the glycoprotein and VI is cholesterol.

(d) 10nm

2 (a) Osmosis: water entering a root cell from the soil

(b) Endocytosis: antibodies being absorbed from milk in the stomach of a newborn baby

(c) Diffusion: oxygen entering a cell in the gill of a salmon

(d) Exocytosis: proteins being secreted from gland cells in the pancreas

(e) Active transport: glucose from digested foods entering cells in the lining of the small intestine

3 (a) i Active transport: move positively charged ions out of the secretory cells

ii) Diffusion: move chloride ions out o the secretory cells

iii) Osmosis: move water out of the secretory cells

(b) Fluid secreted by people with cystic fibrosis is thick and viscous because not enough osmosis occurs. This is due to how the fluid contains secreted proteins and not enough chloride ions in the water to take out these proteins.

4(a) Total area of membranes in liver cell: 98,138µm^2

(b)  Plasma membrane: 1780. So (1780/98,138)*100=1.8%

(c) Inner membrane consists of an extra surface area than the outer membrane for respiration. The outer membrane is smooth whereas the inner membrane is thicker as it shapes itself like a pouch (folded back).

(d) Two main activities of liver cells are protein synthesis and process of ATP. Because of the large amount of rER, this shows how protein synthesis is occurring throughout this cell component. As for the ATP, the large are of mitochondrial membrane indicates a large production of ATP to process the movement of particles in and out of the membrane.

5(a)  Phospholipid bilayers are composed of hydrophilic heads and hydrophobic fatty acid non-polar tails. They consist of cholesterol and integral + peripheral proteins, also glycoproteins as well.

(b) The proteins that binds to the hormone binding sites help cells send and receive messages. Messages pass through the cell when the hormone binds. Neuron synapses are present, which are bound for the receptors. There are also channel proteins which help transfer nerve signals as well.

(c) Vesicles help transport materials through the cell as they can move freely. Vesicles are formed from a small part of the membrane being pinched off. This process is also called endocytosis. These vesicles help transport proteins or substnaces from the rER to the Golgi apparatus. The proteins are then carried off by the vesicles which fuse to the membrane and release these materials outside the cell. This process is also called exocytosis.

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