Biology test

what are the 4 basic mechanisms of transport through the cell membrane?

diffusion and facilitated diffusion- passive osmosis- passive active transport

as a result of diffusion molecules reach ________, where they are evenly spread out; this is where there is no net movement from either side

equilibrium

what is cytolysis?

he dissolution or disruption of cells, especially by an external agent

During osmosis, water moves from the ----- solution (more water, less solutes) to the ----- solution (less water, more solutes).

hypotonic to hypertonic

what is the term for a concentration of water that has reached equilibrium?

isotonic

what is the diffusion through protein channels called? is it passive?

facilitated diffusion yes; molecules go through a protein channel instead of passing through phospholipids

A hypertonic solution has ---- solutes and ---- water than a hypotonic solution

more;less

what does it mean to be passive in terms of movement?

no energy is used to make the cells move; they move solely due to their natural kinetic energy

what are molecules that diffuse through the cell membranes?

oxygen carbon dioxide water

if the particle is solid, endocytosis is also called ?

phagocytosis

if fluid droplets are taken in, the processes is called ?

pinoytosis

how are facilitated diffusion and diffusion different? how are they similar?

In simple diffusion, small noncharged molecules or lipid soluble molecules pass between the phospholipids to enter or leave the cell, moving from areas of high concentration to areas of low concentration (they move down their concentration gradient). Oxygen and carbon dioxide and most lipids enter and leave cells by simple diffusion. In facilitated diffusion, substances move into or out of cells down their concentration gradient through protein channels in the cell membrane. Simple diffusion and facilitated diffusion are similar in that both involve movement down the concentration gradient. The difference is how the substance gets through the cell membrane. In simple diffusion, the substance passes between the phospholipids; in facilitated diffusion there are specialized membrane channels. Charged or polar molecules that cannot fit between the phospholipids generally enter and leave cells through facilitated diffusion.

how is plasmolysis related to turgor pressure?

Plasmolysis is the shrinking of protoplasm away from the cell wall of a plant due to water loss from osmosis, thereby resulting in gaps between the cell wall and cell membrane. When a plant cell is placed in a highly concentrated solution, water diffuses out of the cell, and turgor pressure is lost causing the cell to become flaccid.

are there connections between cells? explain.

When two cells are right next to each other, their cell membranes may actually be touching. A gap junction is an opening from one cell to another. It's not a big opening, but it is large enough for cytoplasm to move from one cell to another. The connections are called channels and they act like tunnels for the movement of molecules.

def. of turgor pressure

the pressure of water pushing the plasma membrane against the cell wall of a plant cell.

what is concentration gradient?

the process of particles moving from an area with a higher number of particles to an area with a lower number of particles. The areas are typically separated by a membrane. (really the difference between the amount of particles on the two sides of the membrane)

what is facilitated diffusion?

the process of spontaneous passive transport of molecules or ions across a cell's membrane via specific transmembrane integral protein

what does the cell do in a hypotonic situation?

water molecules will rush into the cell, and the cell will inflate

-Diffusion -Osmosis -facilitated diffusion -active transport Active/passive? Molecules that move? direction? energy needed? proteins needed?

-diffusion: PASSIVE small, hydrophobic down gradient (towards low concentration) no energy needed no proteins needed -osmosis: PASSIVE water towards high concentration no energy needed no proteins needed -facilitated diffusion: PASSIVE any (specific transporter) down gradient (toward low concentration) no energy needed needs protein -active transport: ACTIVE any (specific transporter) specific: in or out depending on transporter energy needed proteins needed

functions of the cell membrane

-homeostasis -transporting raw materials in and out of the cell -regulating movement of materials -prevents entry of unwanted matter

what are the four factors that determine the rate of diffusion?

1. THE STEEPNESS OF THE CONCENTRATION GRADIENT: the bigger the difference between the two sides of the membrane the quicker the rate of diffusion 2. THE TEMPERATURE: higher temperatures give molecules or ions more energy. The molecules move around faster, so diffusion is faster 3. THE SURFACE AREA: the greater the surface area the faster the diffusion can take place. This is because the more molecules can pass the membrane at any one moment. 4. THE TYPE OF MOLECULES OR ION DIFFUSING: large molecules need more energy to get them to move so they tend to diffuse slowly

what is the difference between a hypotonic and hypertonic solution?

A hypotonic solution is one in which the concentration of solutes is greater inside the cell than outside of it, and a hypertonic solution is one where the concentration of solutes is greater outside the cell than inside it

what is a selectively permeable membrane? the cell membrane is an example of this type of membrane-briefly describe its structure and how it functions.

A selectively permeable cell membrane is one that allows certain molecules or ions to pass through it by means of active or passive transport. It is made up of lipids, proteins and some carbohydrates in a flexible, dynamic and everchanging array. The plasma membrane acts as a selective barrier between the inside and the outside of the cell and controls the exchange of materials between cytoplasm and the surrounding liquid.

why is energy needed in active transport?

It is also possible to move substances across membranes against their concentration gradient (from areas of low concentration to areas of high concentration). Since this is an energetically unfavorable reaction, energy is needed for this movement. The source of energy is the breakdown of ATP. If the energy of ATP is directly used to pump molecules against their concentration gradient, the transport is called primary active transport.

the term fluid mosaic model refers to the cell membrane. What does this mean? what are three "important functions" of the cell membrane?

The fluid mosaic model describes the structure of the plasma membrane as a mosaic of components —including phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character. 1) they keep toxic substances out of the cell; (2) they contain receptors and channels that allow specific molecules, such as ions, nutrients, wastes, and metabolic products, that mediate cellular and extracellular activities to pass between organelles and between the cell and the outside environment; and (3) they separate vital but incompatible metabolic processes conducted within organelles.

what is secondary active transport?

a substance that is being transported without the direct use of ATP along with another substance

what is a contractile vacuole?

a vacuole in some protozoans that expels excess liquid on contraction

what is plasmolysis?

contraction of the protoplast of a plant cell as a result of loss of water from the cell.

what do molecules have which allows them to move about randomly?

kinetic energy

what happens during exocytosis?

large molecules that are manufactured inside the cell are released through the cell membrane

what is osmosis?

the diffusion of water from an area of high concentration to an area of low concentration across a selectively permeable membrane

can water diffuse across the membrane?

yes; it tries to dilute out molecules that can't move across the membrane until the concentration is equal

what is active transport?

the movement of molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy

what is diffusion?

the net movement of molecules from a region of their high concentration to a region of lower concentration

what happens during endocytosis?

the taking in of matter by a living cell by invagination of its membrane to form a vacuole.

what does the cell do in a hypertonic situation?

the water will rush out of the cell, and it will shrivel up. When this happens to a plant cell, it is called a plasmolyzed cell.

why can't molecules like glucose and amino acids diffuse across the phospholipid bilayer? how do they pass?

they are large and polar through protein channels