The Cell and Its Environment Spring 2010

What is a cell? A cell is the basic unit of living things. Some living things are composed of only one cell and are called UNICELLULAR organsims. Organisms that have many different cells are called MULTICELLULAR organisms.

What is the function of a cell? For an organism to live, grow and reproduce an organism must perform processes that allow them to do so. An organism must be able to use energy to live. All living things use energy and different types of organisms obtain energy different ways through the processes of photosynthesis or respiration. Since organisms must use energy there are certain things that have to get into and out of the cell to enable the organism to use or convert energy to a useable form.

Materials that must be able to move INTO ANIMAL cells: 1. Oxygen 2. Water 3. Particles of food

Materials that must be able to move OUT of ANIMAL cells: 1. Carbon dioxide 2. Waste materials

Materials that must move INTO PLANT cells: 1. Sunlight 2. Water 3. Carbon dioxide

Materials that must be able to get OUT of PLANT cells: Oxygen Waste products

What lets stuff in and out of the cell? Cell Membrane Definition- a membrane that controls how materials move into or out of a cell. It acts as a gatekeeper to allow things in and out of the cell. Cell Membrane

What is a cell membrane? Cell membranes are the outside covering of a cell that allows things in and out of the cell. Cell membranes are composed of 3 things: 1. double layer of lipid molecules (fats) 2. transport proteins 3. carbohydrate chains

How does stuff get in and out of the cell? The cell membrane is what allows stuff in and out of the cell. The membrane is selectively permeable. Selectively permeable- Definition- means that some substances can cross the membrane while others cannot.

How does stuff get in and out of the cell? CONT’D Substances that move into and out of a cell do so by means of one of two processes: PASSIVE TRANSPORT or ACTIVE TRANSPORT.

Passive Transport Definition: is the movement of dissolved materials across a cell membrane without using the cells energy. Energy required: NO Type of Transport: PASSIVE

Passive Transport

Diffusion Definition: is the process by which molecules move from an area of higher concentration to an area of lower concentration. Ex: If a bacteria lives in a pond, the water in the pond contains oxygen molecules. The area inside the bacteria cell has a lower amount of oxygen than the pond. So, the oxygen molecules outside of the cell will freely move into the cell.

Diffusion CONT’D Energy required: NO Type of Transport: PASSIVE

Osmosis Definition: is the diffusion of water molecules across a selectively permeable membrane. -Many life processes require water, therefore; all cells must have the appropriate amount of water in them to function. Energy Required: NO Type of Transfer: PASSIVE

Click on link below to see the flow of water during osmosis. /osmosis3.gif /osmosis3.gif

What do cells look like when they have too much or too little water?

Facilitated Diffusion Things like oxygen and carbon dioxide diffuse freely across a cell membrane. Sugar and other molecules do not. Definition: is the process that sugar and other molecules go through to make it easier for them to pass through the cell membrane. The sugar passes through the transport protein “down spouts” into the cell. Energy Required: NO Type of Transfer: PASSIVE

Facilitated Diffusion CONT’D

Active Transport Sometimes cells need materials to flow the opposite direction of the flow of diffusion. In this case the cell would need to use ACTIVE TRANSPORT to carry these materials in and out. DEFINITON: is the movement of materials a cross a cell membrane using cellular energy. The cell uses its’ energy so the transport proteins “pick up” materials and “carry” them across the membrane. Examples of substances that are carried in and out of the cell this way are: calcium, potassium, and sodium. ENERGY REQUIRED: YES TYPE OF TRANSPORT: ACTIVE

Active Transport