cells and their environment
TRANSCRIPT
Cells and Their Environment
9-11 LS 1D: the cell is surrounded by a membrane that separates the interior of the cell from the outside world and determines which substances may enter and which may leave the cell. 9-11 Sys C: As something new is introduced or a part of the system is changed, new and sometimes unpredictable properties of the system will emerge. We can create simplified models of complex systems to predict possible results.
Cell Theory Remember from our last set of notes, that the
importance of cells to living organisms is summarized in the cell theory:
1. The cell is the basic unit of structure and function in living things.
2. All organisms are composed of cells and/or cell products.
3. All cells come from other cells.
Types of cells Cells are divided into two categories based on
their level of complexity (simple or complex). A.Prokaryotes: Cells that lack membrane-
bound organelles B.Eukaryotes: Complex cells that contain
membrane-bound organelles. 1. These organelles are smaller structures within
cells that have specific roles to keep the cell alive. a. Just like the organs in animals.
Prokaryotes & Eukaryotes 1. Organisms composed of simple cells
(prokaryotic cells) are called “prokaryotes”: a. Bacteria b. Blue-green algae 2. Organisms composed of complex cells
(eukaryotic cells) are called “eukaryotes”: a. Humans b. Insects c. Plants d. Trees
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Homeostasis
Remember that balance and homeostasis mean the same thing.
Definition: The process of maintaining a constant internal environment despite changing external conditions. Examples: A. Concentration of water B. Temperature regulation C. Concentration of glucose, waste and gases in cells
Movement of substances into and out of cells.
Because cells are living things, there needs to be a supply of materials coming in and the removal of waste products out of the cell to keep it healthy and maintain it’s homeostasis.
Movement of these substances happens in two ways: 1. Passive Transport: Movement of substances
without using cellular energy 2. Active Transport: Movement of substances
requiring the cell to use energy.
Passive Transport The way the smell of fresh cookies travels
throughout the house is an example of the random movement of molecules. 1. Molecules tend to move from areas of high
concentration to areas of lower concentration. 2. This will continue until they are evenly spread
out, or in other words, when they have reached a state of EQUILIBRIUM.
3. The two examples of this are: a. Diffusion b. Osmosis
Review on Solutions Solutions are mixtures of different
substances: Solvent: the medium in which a substance is
dissolved. Solute: the substance dissolved in the solvent. Solution: the uniform mixture of the solute and
solvent. For example, a glass of Kool-Aid Solvent= Water Solute= sugar and powder mix
Passive Transport
#1. Diffusion: The movement of molecules from areas of high concentration to areas of low concentration.
Diffusion
One important part of diffusion is that the motion of the molecules
is random. As they collide into each other, they become more
and more spaced out….thus becoming equally spaced.
EQUILIBRIUM!
Passive Transport
#2. Osmosis: This is a specific type of diffusion Def: The movement of water across a membrane
from an area of high concentration of water to an area of lower water concentration.
Osmosis To fully understand and be able to predict
the changes due to osmosis, we need to remember what a solution is:
What are the parts of a solution? * Solute * Solvent
Osmosis
To understand the changes that will occur due to osmosis, we need to understand the concentrations of solvents & solutes on either side of the membrane (or barrier).
Active Transport Cellular energy is very valuable, so cells
will not use energy for transport unless they need to.
Since this goes against the concentration gradient, it is like pushing something up hill instead of letting it roll downhill.
Structure of the Cell Membrane
The structure of the cell membrane includes channels through which materials can pass.
How Do Materials Move In & Out Of The Cell? Materials like glucose, water, solutes and
oxygen can move through the cell membrane in one of two ways:
1. Between the phospholipids 2. Through a channel protein
Moving Between Phospholipids
There is a small amount of space between the round heads of the phospholipids that make up a majority of the cell membrane.
Moving Through Channel Proteins Channel proteins allow larger molecules to
pass through. a. Sugars, amino acids, small proteins. b. Molecules “too big” to fit between
phospholipids.
The effects of diffusion & osmosis on living cells. Both diffusion and osmosis will result in
changes to living cells. The movement of water & other solutes
back and forth across the membrane will change the volume and pressure inside of the cell.
Since plant cells are surrounded by a rigid outer layer, the overall shape will NOT change, but the pressure inside will.
Diffusion/Osmosis and Cells Solutions are classified in 3 ways based
on their concentrations of water in relation to the inside of cells Hypertonic: Higher H2O concentration
inside cell. Hypotonic: Higher H2O concentration
outside of cell. Isotonic: Equal concentrations of H2O
inside and outside of cells.
Diffusion/Osmosis and Cells
In hypertonic solutions, animal cells will loose water because The water inside is a higher concentration outside. The rules of diffusion/osmosis say that water will move from the area of high concentration to low concentration
Diffusion/Osmosis and Cells
In hypotonic solutions, animal cells will gain water because The water inside is a lower concentration than outside. The rules of diffusion/osmosis say that water will move from the area of high concentration to low concentration
Diffusion/Osmosis and Cells
In isotonic solutions, animal cells will have no net change because the water inside is equal to the concentration outside. The rules of diffusion/osmosis say that water will move from the area of high concentration to low concentration
Diffusion/Osmosis and Cells Another way to look at it in animal cells
Hypotonic Isotonic Hypertonic
Diffusion/Osmosis and Cells In plant cells, the differences are not as
obvious. Think of a plant cell as being a “balloon in a box”. If you blow up the balloon inside the box, it will
fill the area, and then no longer be able to expand any more….it will contain a huge amount of internal pressure.
If you release the air from that balloon, the overall size of the box won’t change, but the pressure of the balloon inside will be very small, making the balloon flimsy and soft.
Pictures of plant cells in different tonicities (concentrations) of solutions