Chapter 2

Interaction of Cell Structures

Transport Mechanisms• are ways in which materials enter or leave the cell.• crucial in transport is the...

Structure of the Cell MembraneThe cell membrane functions:• to protect • to contain the cell parts• to regulate what materials go in and out.

• It’s structure allows it to do this.

• it is a double membrane (2 layers) of phospholipid molecules

• (refer to diagram page 51-2)

phosphate heads (B):• polar and is attracted to water (hydrophilic)• this end able to dissolve in water

lipid tails (A):• Non-polar fatty acids not attracted to water (hydrophobic)• they are insoluble in water

• This arrangement of polar heads facing outside and nonpolar lipid tails facing inside is what allows the cell membrane to act as a barrier between the tissue fluid (extracellular fluid) and the cytoplasm (intracellular fluid) of the cell. https://www.youtube.

com/watch?v=S7CJ7xZOjm0 – cell membrane – bozeman ~11mins

Animations describing Passive and Active Transport

Great descriptive animation on;

Passive and Active Transport:• http://www.northland.cc.mn.us/biology/Biology1111/animations/transport1.html - doesn’t work

• http://www.northland.cc.mn.us/biology/Biology1111/animations/index_page_for_animations.htm - doesn’t work

Lysosome Animation:• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__lysosomes.html

Osmosis Animation:• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

Facilitated Difussion Animation:• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/

animation__how_facilitated_diffusion_works.html

Difusion Animation:• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

What substances pass across a cell membrane freely?

• Thus, water, oxygen and carbon dioxide can pass through the cell membrane freely. • Other substances, like big glucose molecules or ions must pass through specialized

transport proteins. • Transport mechanisms may be:

A. passive (3 types)1. Diffusion2. Osmosis3. Facilitated Diffusion

B. activeC. bulk (creation of vesicles) (2 types)

1. Endocytosis2. Exocytosis

A. Passive Transport (3 types)1. Diffusion• Move via brownian motion (randomly moving particles) Ex. perfume

diffuses throughout a room• materials diffuse from an area where there is a lot (greater

concentration) to an area where there is less (lower conc.)• requires no additional energy • in a closed system, materials will diffuse until they are scattered evenly

throughout. • if the substance is colored, the color fades as diffusion continues.• diffusing materials may be solid, liquid or gaseous.• Good for short distances, and for small, uncharged molecules (oxygen

and carbon dioxide)

Question: Once equilibrium is reached, does diffusion stop?Difusion Animation: http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

Which cell is most efficient at taking in nutrients?

Surface Area to Volume Ratio: (refer to handout)

• Having a large surface area relative to its volume increases the area available for materials to diffuse in and out of a cell.

• The smaller the surface area/volume ratio, the bigger the cell and the less efficient it will be to diffuse enough materials in to serve the mass of the cell.

• Thus when the cell reaches a size where diffusion becomes inefficient, it divides.

• Now two small cells have formed, thus increasing the surface/volume ratio and diffusion efficiency.

A. Passive Transport (3 types)

2. Osmosis• Some membranes only allow certain materials to pass through. • The membrane is said to be selectively or semi-permeable. • When a liquid, usually water, is passing through a selectively

permeable membrane, the process is called osmosis.– requires no energy– operates from high -> low concentration (ie. ‘along’ the

concentration gradient)– continues until the concentration is the same on both sides of the

membrane (ie. equilibrium is reached)

http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

Water, starch, and iodine demo

Diffusion is occurring with: a) water molecules• water diffuses into the bag in an attempt to equalize the • concentration on both sides (obtain equilibrium). Bag

swells.

b) iodine molecules• iodine diffuses into the bag, reacting with starch,

observable as a color change from red-brown to blue- black, but...

Demo cont’d

• Some molecules, eg. starch, are too big to diffuse through the bag. The water outside remains the red/brown color of iodine indicating a negative test. (Starch turns blue/black in the presence of iodine.)

• Osmosis continues even after equilibrium is reached. Molecules are then diffusing in at the same rate as they are diffusing out.

• We say that osmosis is dynamic.

Let’s suppose: our cells are being bathed in tissue fluid.

• Materials the cells need, glucose, oxygen, etc., diffuse from the blood vessel capillaries into the tissue fluid, then across the cell membrane into the cells.

• Waste products in the cells diffuse out of the cells, into the tissue fluid and into the blood vessels.

• How will the direction of water flow be affected if the solute concentration outside the cell is:– higher than inside the cell?– lower than inside the cell?– the same as inside the cell?

Objective 3

• The terms hypertonic, hypotonic, and isotonic refer to the solute concentration of a solution.

Hypertonic

• When cells are placed in a hypertonic solution, we label the solution hypertonic and the cytoplasm of the cell hypotonic

• There is a greater concentration of solute outside and a greater concentration of water inside

• Important rule: Water always moves from a HYPOTONIC area to a HYPERTONIC area

• So, water will diffuse out of the cell, to where the water concentration is less

• This will continue until equilibrium is reached. • Because the cell loses water, it will shrink.

Hypotonic

• The solution is hypotonic to the cell cytoplasm, so we label the cell hypertonic.

• The cell has more solute and less water, so water will move into the cell until equilibrium is reached.

• The cell will swell and may burst before that happens.

Isotonic

• The solute concentration is the same on both sides of the cell membrane.

• Osmosis continues with water diffusing into the cell at the same rate as it is diffusing out.

• No observable change in cell size.• The cell cannot prevent this

movement of water because it is permeable to water molecules.

What type of solution is in this example?Explain how you know.

Objective 4

• Refer to page 55 in text to compare all three osmotic conditions in animal and plant cells, paying particular attention to the role played by the cell wall in plant cells. (I will use shoe box / balloon for demo later).)

• Students do web link page 57.

Animal cells and plant cells

Objective 4 answer (include diagram too from previous slide)

• Hypotonic environment– Animal cells – take in water, may burst– Plant cells – take in water, cell wall protects from

bursting• Hypertonic environment– Animal cells – water leaves cells, may shrivel– Plant cells – water leaves cell, cytoplasm shrinks,

membrane separates from cell wall (plasmolyzed)

3. Facilitated Diffusion

• Substances that cannot diffuse through the phospholipid layer of the membrane

• (eg. Molecules that are too big, insoluble in the lipid layer, or charged ions)

• may be transported with the help of specialized transport proteins (refer to p.52)

• Each transport protein will help only one type of molecule, depending on its shape, size and electrical charge.

Two types of transport proteins include:

• carrier proteins– accepts only non-charged particles; eg. Glucose– allows the particles to move in or out of cell (see

diagram p.57)– changes shape (rocking motion) to transport

molecule

3. Facilitated Diffusion

Carrier Protein - http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html

• channel proteins– accepts charged particles that are opposite in charge to

itself; ie. a negative channel protein accepts a positively charged particle (note Bio Fact p. 58 in text)

– has tunnel shape that allows the particle to pass through

Reminder: Since no energy is required and materials move along the concentration gradient, diffusion, osmosis and facilitated diffusion are all forms of passive transport.

3. Facilitated Diffusion

https://www.youtube.com/watch?v=doxfuV3tqDA

Let’s review: Which is which?

Channel Protein Carrier Protein

B. Active Transport• A cell may need to concentrate nutrients for growth inside,

completely rid itself of toxic wastes to the outside or create an electrical potential across a membrane to allow nerves and muscles to work (see square bullets p.59 for more examples).

• Passive transport would not be sufficient for this. • In active transport...

– materials move against the concn gradient (low -> high)– energy is required ( in the form of ATP) – Transport proteins are used to make active transport pumps,(like fac. diff. but

against the concn gradient.) – eg. the sodium-potassium pump allows sodium ions to leave and potassium

ions to enter a cell by changing the shape of a transport protein, with the help of an ATP energy molecule.

– See diagram p.60 for detailshttps://www.youtube.com/watch?v=P-imDC1txWw

C. Bulk Transport (vesicles)

• Macromolecules may be too big or too polar to be transported by passive or active transport.

• The cell membrane folds in on itself to create a membrane-enclosed, bubble-like sac,or vesicle.

• The cell may use these vesicles to take materials in (endocytosis) and expel them out (exocytosis). See p.62-64.

https://www.youtube.com/watch?v=DuDmvlbpjHQ

Endocytosis has three forms:

1. pinocytosis (“cell-drinking”)• a vesicle is created involving the intake of a small droplet of tissue

fluid, together with any dissolved substances or very small particles it may contain.

• occurs in nearly all cell types all the time (See p. 62)

2. phagoctosis (cell-eating)• a vesicle is created involving the intake of a large droplet of tissue

fluid and matter such as bacteria or bits of organic matter; digestive enzymes are necessary to digest the matter

• occurs only in specialized cells; eg. amoeba or macrophages (white blood cells) of our immune system

3. receptor-assisted endocytosis • vesicles are created when special molecules with ‘tags’

bond to matching ‘receptors’ on the cell membrane;• once inside the vesicle splits in two parts - one carrying

receptors returns, once again, to become part of the cell membrane and the other, containing the food molecule, empties into the cell cytoplasm

• membrane receptors fit the shape of only one specific molecule; eg. cholesterol (See diagram page 63)

https://www.youtube.com/watch?v=knJQzBmqOZw

https://www.youtube.com/watch?v=X8Z0jW7XKHs – student stop-motion (good)

Exocytosis

• a vesicle is formed using membrane from an organelle;

• eg. ER, golgi apparatus• the vesicle moves to the cell

surface, joins the cell membrane, emptying (secreting) its contents into the tissue fluid

• eg. the pancreas secreting the hormone insulin

Objective 5 & 6

• Surface area to volume demo - https://w ww.youtube.com/watch?v

=xuG4ZZ1GbzI The Limits of Cell Size - P. 55• Post-Lab questions 1-3; • conclude and apply questions 4 & 5

• http://learn.genetics.utah.edu/content/cells/insideacell/ - cell organelles

• https://www.wisc-online.com/learn/natural-science/life-science/ap11604/identifying-eukaryotic-animal-cell-organelles - good too

• Note: Both review sheets – correct• Surface area review activity• Hand back assignments• Other resources for review

Chapter 3 – Energy for CellsPhotosynthesis(Page 73)

• All living things need energy to grow and carry out all other life processes.

• Some organisms can trap energy directly from the sun and make them into organic compounds, and so are termed autotrophic (self-feeding).

• They make their own food in a process called photosynthesis.

Photosynthesis(Page 73)

• In green plants, mostly the leaves, the chloroplasts in the plant cells are the site for photosynthesis.

• Photosynthesis combines carbon dioxide and water, in the presence of sunlight, to produce a carbohydrate (usually glucose, a sugar);

• ie. light energy is converted to stored chemical energy in the bonds of carbohydrate molecules. A by-product is oxygen.

Photosynthesis(Page 73)

light energy6CO2 + 6H2O --------> C6H12O6 + 6O2

carbon dioxide + water -------> glucose + oxygen

• Organisms that cannot make their own food, but instead must consume plants, or animals to get the energy they need are called heterotrophs.

Aerobic Cellular Respiration(Pages 82-5)

• The energy trapped in plant carbohydrates (starches and sugars) has to be released in animal cells before those cells can use it to function.

• This process occurs in the mitochondria of cells and is called cellular respiration.

• In the mitochondria, carbohydrates (glucose), are broken down (metabolized) and combined with oxygen in a series of chemical reactions to release energy.

Cellular Respiration

C6H12O6 + 6O2 -------> 6CO2 + 6H2O+ ATP

glucose + oxygen carbon dioxide + water +energy

ATP • adenosine triphosphate• an energy carrier (like a battery) that stores the released energy

and carries it to where it is needed in the cell to do work. • eg. active transport, produce proteins, contract a muscle cell,

etc.• All organisms perform cellular respiration and almost all

organisms carry out the process of aerobic cellular respiration in their mitochondria.

• Aerobic (‘ae’ refers to air or oxygen) means that the process requires oxygen.

Note: • Photosynthesis and cellular respiration are complementary

processes. • The reactants of one are the products for the other. • Photosynthesis stores energy and cell respiration releases

energy. • Together they drive the carbon cycle. • Carbon, the basic element of most living things, enters living

systems through photosynthesis in the making of the carbohydrate and some of the carbon returns to the atmosphere through cell respiration in the formation of CO2.

Global Implications - (Pages 86-90)

• The earth is a closed system; little or no matter comes in from the outside.

• The processes of photosynthesis and aerobic respiration have great importance to our world:

1. to sustain life• to sustain life, nutrients are moved through a series of

cycles, the carbon cycle being one of them. • Photosynthesis and respiration are the two ‘halves’ of

the living component of the carbon cycle :

(i) on land —> photosynthesis takes carbon from CO2 and forms organic molecules, carbohydrates), for use in life processes and respiration breaks them down releasing energy and returning CO2 to the atmosphere once again.

(ii) in oceanic water —> CO2 dissolves in oceanic water to form carbonic acid which breaks down to form bicarbonate ions = the source of carbon for aquatic plants to carry out photosynthesis.

2. in industry• photosyn. is the biological basis for the

primary industries of the world.

(a) agriculture and (b) forestry• These involve the harvesting of plants / plant

materials for food, construction, paper, fabrics, cosmetics, medicines, personal care products.

Global Implications - (Pages 86-90)

(c) fisheries• The fisheries depend on aquatic autotrophs as the basis of the

aquatic food chain to feed the species they wish to catch (herring, turbot, lobster)

(d) Mining• the mining of fossil fuels has its beginnings when the petroleum

and coal of today were the oceanic beds and ancient forests millions of years ago.

• Petrochemicals are the source of fuels (95%) and plastics, cosmetics, detergents, drugs, synthetic fibers like nylon, and synthetic rubber.

3. on the environment• The carbon cycle is different today than it was in the

past:– 1850: 28 ppm or 0.028 % by volume– Today: 350 ppm or 0.035%

• The increase in CO2 levels is an important factor in global warming and is due to:– society’s dependence on fossil fuels as an energy source and– the removal and burning of vast stands of trees that

otherwise would absorb CO2 in photosynthesis.

Global Implications - (Pages 86-90)

Discussion Question:• How have human activities affected the

processes of photosynthesis and respiration through– chemicals ?– pollution ?– selective breeding ?– genetic engineering ?– other ?