Key Idea #11

Cells in multicellular organisms are specialized to take in nutrients, which are used to make the materials that a cell or organism needs.

Nutrients taken in by the cell provide materials to build

cell structures (organelles) and specialized molecules used by the

organisms: – carbohydrates– lipids (fats)– proteins– nucleic acids: DNA and RNA

Organic and Inorganic Compounds

Organic Compounds– contain carbon

• include carbohydrates, proteins, lipids, and nucleic acids

Inorganic Compounds– do not contain carbon*

• includes water, sodium chloride (table salt) and carbon dioxide* - an exception

Carbon dioxide and water are used to produce carbohydrates, proteins and fats (lipids).

http://library.thinkquest.org/C004535/media/cell_membrane.gif

Carbohydrates

are energy-rich compounds made of the elements carbon, hydrogen, and oxygen

are an important part of cell membranes and cell walls

include sugars– fruits and some vegetables

include starches– potatoes, noodles, rice, and bread contain starch that your

body breaks down into glucose (a sugar)

Proteins

are large organic molecules make of carbon, hydrogen, oxygen, nitrogen and sulfur.

are found in foods such as meats, eggs, fish, nuts and beans

form parts of cell membranes make up many of the organelles found in cell are used by cells in your body to build body parts

such as hair.

Lipids

are energy-rich compounds made of carbon, hydrogen, and oxygen.

include fats, oils, and waxes. includes cholesterol

– an important part of animal cell membranes– Meat, cheese, and eggs are all high in cholesterol

Nucleic Acids

are very large organic molecules made of carbon, oxygen, hydrogen, nitrogen, and phosphorus.

contain the instructions needed to carry out life.– DNA

• genetic material that contains the information that is passed from parent to offspring

– RNA• important for protein production• found in the cytoplasm and nucleus

Water

must be present for most chemical reactions to take place.

helps cells keep their size and shape

Diffusion and Osmosis

Cell Membrane acts as a gatekeeper is selectively permeable

– controls what substances can enter or leave the cell

is permeable to oxygen, water, and carbon dioxide to pass through it

is not permeable to some large molecules and salts

Substances that can move into and out of a cell use one of three methods:

Diffusion Osmosis Active Transport

Diffusion – Molecules in Motion Diffusion is the main method by which small

molecules move from an area of higher concentration to an area of lower concentration.

http://www.mrphome.net/physics/diffusion/index.html

What causes diffusion?

Molecules bump into each other and eventually spread out evenly throughout an area.– Example: Air freshener spreads out when

you spray it.

When there is a higher concentration of molecules outside a cell than inside a cell

the molecules diffuse (move) into the cell until there is an equal number of molecules inside and outside the cell.

These molecules can be oxygen, carbon dioxide or water

http://www.indiana.edu/~phys215/lecture/lecnotes/lecgraphics/diffusion.gif

When the molecules are equal on both sides of the cell membrane, it is called equilibrium.

Googleimages.com

Osmosis is a type of diffusion.

is the diffusion of water molecules through a selectively permeable membrane.

is important to cells because they can’t function properly without adequate water.

http://www.biologycorner.com/resources/osmosis.gif

Note: Only water molecules pass through the membrane during osmosis

occurs when water molecules move from an area of higher water concentration to an area of lower water concentration until equilibrium is reached.

Note: other dissolved particles can’t pass through the membrane

FYI:

A simple rule to remember is:                                

http://www.biologycorner.com/bio1/diffusion.html

This is why •you get thirsty after eating something salty because the excess salt draws water to the cells in the body.

•people lost at sea will speed up dehydration (and their death) by drinking sea water.

•“salting fields" was a common tactic used during wars to cause food shortages.

When salt is concentrated inside or outside the cell membrane, it will draw the water in its direction.

Osmosis & different concentrations of solute:

In normal cells:

the amount of dissolved salt molecules is equal on both sides of the cell membrane.

the water moves back and forth but the overall amount of water on either side remains the same.

http://www.biologycorner.com/bio1/diffusion.html

When there are more dissolved salt molecules inside the cell than outside the cell:

water moves into the cell since “salt sucks”.

the cell grows larger.

http://www.biologycorner.com/bio1/diffusion.html

In plant cells this causes

the central vacuoles to fill with water and the plant becomes rigid.

Note: The cell wall keeps the plant from bursting.

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/aplantturgor.gif

In animal cells

the cells may be in danger of bursting.

contractile vacuoles pump water out of the cell to prevent this.

Googleimages.com

When there are more salt molecules outside the cell than inside the cell

the water is sucked outside the cell.

the cell shrinks.

http://www.biologycorner.com/bio1/diffusion.html

In plant cells, the central vacuole loses water and the cells shrink, causing wilting.

In animal cells, the cells also shrink and shrivel up.

In both cases, the cell may die.

FYI: Why can’t fish live in both fresh and salt water?

Salt water fish have cells that don’t

contain as much salt as the salt water they live in

cells lose a lot of water into the water around them by osmosis

must drink a lot of water and produce little urine to compensate

Fresh water fish have cells that contain

more salt than the fresh water they live in

cells gain water from their surroundings by osmosis

don’t usually drink water and produce large amounts of urine to compensate

Substances move in and out of cells by

passive transport– no energy is needed

• diffusion• osmosis

active transport – cell uses energy (ATP)

• engulfing• contraction of vacuole wall eliminates waste• transport proteins in the cell membrane pick up

molecules outside the cell and carry them in

http://www.dwm.ks.edu.tw/bio/activelearner/05/images/ch05summary.jpg

Nutrients that can’t pass through the cell membrane by diffusion can be taken into the cell through active transport.

Active transport uses the cells energy to accomplish this.

Active Transport

Active transport examples: engulfing

transport proteins in the cell membrane pick up molecules outside the cell and carry them in

http://www.nicksnowden.net/images/Membranes_and_Transport/endocytosis.gif ; phschool.com.jpg