L 4 cell membrane and cell transport

briefly describe the cell membrane

-Biological membrane

-Separates interior of cell from environment -Selectively permeable to ions and organic molecules

-Controls movement of substances in and out of cells

-Protects cell from outside forces,helps maintain homeostasis

cell membrane

phospholipid bilayer with embedded proteins that controls the passage of organic molecules, ions, water, and oxygen into and out of the cell. Wastes (such as carbon dioxide and ammonia) also leave the cell by passing through the membrane

what are biomolecules produced by?

living things and also referred to as organic molecules

what element do all biomolecules contain?

carbon

what are the 4 types of biomolecules

carbohydrates

lipids

proteins

nucleic acids (DNA and RNA)

what are lipids composed of?

Lipids are hydrophobic compounds composed of carbon, hydrogen and oxygen.

what is the main structural component of cell membranes

phospholipid

what is a phospholipid a combination of ?

A phospholipid is a combination of a phosphate group and two fatty acids which together form a tadpole -shaped molecule with a phosphate head and a lipid tail.

describe the head of a phospholipid

They have a polar hydrophilic head (the negatively-charged phosphate group)

describe the tail of a phospholipid

"non -polar hydrophobic ""tails"" (the fatty acid chains). - They are the main components of cell membranes."

what solution is both inside and outside the membrane

there is a watery solution both inside and outside the membrane

what is the phospholipid bilayer?

The phospholipids line up with the heads out and the tails in forming a double layer

what is the structure of the cell membrane described as?

fluid mosaic

where can proteins be found in the cell membrane?

spanning the whole membrane -integral

peripheral proteins (near the surface)

surface proteins

where are carbohydrates found

Carbohydrates are found on the outer surface of all eukaryotic cell membranes, and are attached to the membrane proteins or sometimes to the phospholipids.

glycoproteins

proteins with carbohydrates attached

glycolipids

phospholipids with carbohydrates attached

what are carbohydrates important for

cell recognition

what do animal cell mmebranes contains that link fatty acids together

Animal cell membranes contain cholesterol linking the fatty acids together and stabilising and strengthening the membrane

where do cells aquire the molecules and ions they need

All cells acquire the molecules and ions they need from their surrounding extracellular fluid

what is there constant traffic of

Thus there is constant traffic of molecules and ions in and out of the cell through the cell membrane Examples: glucose, ions such as Na+, Ca2+

are cell membranes selectively permeable

yes

what does selectively permeable mean

they admit some subatnce but not others

factors that influence permeability

particle size

polarity

electrical charge

3 types of passive transport

simple diffusionosmosis-diffusion of waterfacilitated diffusion-diffusion with the help of a membrane protein

diffusion

the movement of atoms,ions and/or molecules down a concentration gradient

from an area of high concentration to an area of low concentration

what types of matter does diffusion occur in

gases liquids solids

when happens in the pricess of diffusion in the event of high cocnnetration particles

in the event of high concentration particles will diffuse or disperse to the lower or less concentrated region until a random distribution occurs.

dynamic equilibrium

This means movement will continue as before but there is no net movement in any one direction

concentration of oxygen in the alveoli

In the lungs there is a higher concentration of O2 in inhaled air in the alveoli than in the surrounding blood capillaries.

how does oxygen diffuse in alveolus

O2 diffuses from the alveolus into the blood.

concentration of co2 in blood capillaries

Similarly there is a higher concentration of CO2 in the blood capillaries than in the alveoli, thus CO2 diffuses from the blood into the alveoli and is exhaled

Gas exchange in the lungs

In the lungs there is a higher concentration of O2 in inhaled air in the alveoli than in the surrounding blood capillaries

O2 diffuses from the alveolus into the blood

there is a higher concentration of CO2 in the blood capillaries than in the alveoli

CO2 diffuses from the blood into the alveoli and is exhaled

Gas exchange in plants

Gases enter and leave plants through stomata tiny pores in the surface of a leaf.

The O2 produced in photosynthesis is at a high concentration in the leaf and thus diffuses to the outside air which has a low concentration of O2.

CO2 is at a high concentration in the outside air and diffuses into the leaf where there is a low concentration of CO2

how do gases enter and leave plants

Gases enter and leave plants through stomata tiny pores in the surface of a leaf.

describe the oxygen produced in photosynthesis

The O2 produced in photosynthesis is at a high concentration in the leaf and diffuses to the outside air which has a low concentration of O2.

describe the co2 produced in a plant

CO2 is at a high concentration in the outside air and thus diffuses into the leaf where there is a low concentration of CO

osmosis

Osmosis is the 'diffusion of' or 'movement of' water across a semi permeable membrane from a region of high water concentration to a region of low water concentration

water potential

Osmosis can be quantified using water potential,

so we can calculate which way water will move, and how fast. Water potential is simply the effective concentration of water so water will move from high water potential to a lower water potential.

osmotic pressure

a measure of the force that must be applied to stop the osmotic movement of water across a membrane.

Osmotic pressure is dependent on the solute concentration

more solutes more pressure

less solutes less pressure

what type of solutions can cells be placed in

Cells can be placed in solutions of different concentrations relative within the cell

hypertonic solution

a solution where the concentration of solute is higher outside than within the cell.

hypotonic solution

a solution where the concentration of solute is higher inside the cell than outside the cell

describe a hypertonic solution

The movement of water will therefore be from high water to low water concentration

water will exit the cell.

In animal cells the cell will shrivel while in plants the cell membrane will pull away from the cell wall in what is termed plasmolysis

plasmolysis

In animal cells the cell will shrivel while in plants the cell membrane will pull away from the cell wall

isotonic solution

Solute concentration is equal inside and outside of the cell cells maintain an isotonic environment-controlled by the cell membrane

describe a hypotonic solution

The movement of water will therefore be from high water to low water conc. i.e water will enter the cell. In animal cells the cell will burst, while in plant cells, due to the cell wall, the cell will swell or become turgid.i.e more turgor pressure

uptake of water by plant root cells

When the concentration of water in soil is higher than in plant root cells, water moves from soil to plants by osmosis

absorption of water in the large intestine

As food moves through the digestive tract a considerable volume of water has been added to it in the digestive juices.In order to maintain the required water concentration in the body, this water needs to be recovered.This happens in the large intestine where water moves into the bloodstream by osmosis

reabsorption of water in the kidney

Blood is filtered in the kidneys.

As the filtrate moves through the kidney tubules most of the water is reabsorbed back into the blood by osmosis and does not form part of the urine made.

The amount of water reabsorbed depends on the osmotic potential of the blood- the concentration of water in the blood at that time.

examples of osmosis in biological systems

1. Uptake of water by plant root cells.

2. Absorption of water in the large intestine

3. Reabsorption of water in the kidney

facilitated diffusion

This involves the movement of molecules across a membrane with the assistance of integral proteins within the membrane.

Movement is similar to simple diffusion in that molecules move from a region of high concentration to a region of lower concentration and does not require energy .

what are the 2 kinds of transport protein

channel proteins carrier proteins

channel proteins

Channel Proteins form a water-filled pore or channel in the membrane.

This allows charged substances usually ions to diffuse across membranes.

Most channels can be gated (opened or closed) allowing the cell to control the entry and exit of ions.

carrier proteins

Carrier Proteins have a binding site for a specific solute and constantly flip between two states so that the site is alternately open to opposite sides of the membrane. The substance will bind on the side where it at a high concentration and be released where it is at a low concentration

what direction can facilitated diffusion take place

Facilitated diffusion can take place in both directions with the same carrier protein. it depends on the conc on each side of the membrane.

what does active transport require

requires the cell to expend energy in the form of ATP.

active transport

In active transport materials are moved against the concentration gradient, from where they are less concentrated to where they are more concentrated.

2 types of active transport mechanisms

1. Ion pumps.special cell membrane proteins 2. Endocytosis/exocytosis

cell membrane ion pumps

These are special integral or trans-membrane proteins

The protein binds a molecule of the substance to be transported on one side of the membrane, changes shape, and releases it on the other side

The proteins are highly specific, so there is a different protein pump for each molecule to be transported

example of an ion pump

The best-known and most understood cell membrane ion pump mechanism is the sodium -potassium (Na+K+) pump. This transport protein is present in the cell membranes of all animal cells ▪The Na+K+ pump actively pumps 3 sodium (Na+) ions out of the cell and simultaneously pumps 2 potassium (K+) into the cell . ATP is used to provide energy as the ions are moving against the concentration gradient (from low to high) ▪This helps establish a net charge across the cell membrane with the interior of the cell being negatively charged with respect to the exterior. ▪This is called a 'resting potential' and prepares nerve and muscle cells for the propagation of action potentials leading to nerve impulses and muscle contraction. ▪ Another important effect of this pump is that the accumulation of sodium ions outside of the cell draws water out of the cell and thus enables it to maintain osmotic balance (otherwise it would swell and burst from the inward diffusion of water)....i.e. isotonic ▪ Almost one-third of all the energy generated by the mitochondria (in respiration)in animal cells is used just to run this Na+K+ pump

what are the types of endocytosis

phagocytosispiocytosis

phagocytosis

the type of endocytosis where a large particle or even a whole cell is engulfed An example is the way white blood cells can engulf entire bacterial cells as part of our defence system. Phagocytosis is also the way in which some single-celled organisms (e.g. Amoeba) feed

pinocytosis

when some external fluid or a small food particle/solute is engulfed. The resulting vesicle formed is much smaller than in phagocytosis

exocytosis

is the reverse process of endocytosis used to expel substances from the cell (either waste or sometimes products, e.g. this process used for secreting some hormones) During exocytosis a vesicle moves to the cell membrane, fuses with it, and then releases its contents to the outside of the cell.

what happens in endocytosis

the cell engulfs some extracellular fluid including material dissolved or suspended in it.

A portion of the cell membrane is indented and pinched off forming a membrane-bounded vesicle

Endocytosis/exocytosis

•The cell membrane pumps discussed above are involved in the passage of relatively small molecules across cell membranes. Larger molecules and sometimes even whole cells cross cell membranes by endocytosis (in) and exocytosis (out)