Unit 2 Flex Review

A1. describe the following cell structures and their functions:

Part Functioncell membrane ● selectively permeable – allows entry/exit of certain molecules/substances

● has tags (antigen) used to identify cells

mitochondria The “powerhouses” of the cell, mitochondria are oval-shaped organelles found in most eukaryotic cells. As the site of cellular respiration, mitochondria serve to transform molecules such as glucose into an energy molecule known as ATP (adenosine triphosphate). ATP fuels cellular processes by breaking its high-energy chemical bonds. Mitochondria are most plentiful in cells that require significant amounts of energy to function, such as liver and muscle cells.

Smooth & Rough endoplasmic reticulum

The endoplasmic reticulum (ER) is a membranous organelle that shares part of its membrane with that of the nucleus. Some portions of the ER, known as the rough ER, are studded with ribosomes and are involved with protein manufacture. The rest of the organelle is referred to as the smooth ER and serves to produce vital lipids (fats).

ribosomes Ribosomes are the protein factories of the cell. Composed of two subunits, they can be found floating freely in the cell’s cytoplasm or embedded within the endoplasmic reticulum. Using the templates and instructions provided by two different types of RNA, ribosomes synthesize a variety of proteins that are essential to the survival of the cell.

Golgi bodies If the proteins from the rough ER require further modification, they are transported to the Golgi apparatus (or Golgi complex). Like the ER, the Golgi apparatus is composed of folded membranes. It searches the protein’s amino acid sequences for specialized “codes” and modifies them accordingly. These processed proteins are then stored in the Golgi or packed in vesicles to be shipped elsewhere in the cell.

vesicles Small membranous sacs. Usually are used to transport substances from one part of the cell to another (ex. transport vesicle – transports proteins from the rough ER to the golgi apparatus).

vacuoles Small membranous sacs. Usually are used to store substances within a cell. (ex. plants use vacuoles to store proteins, starches, or water (central vacuoles).

lysosomes Lysosomes are organelles that contain digestive enzymes. They digest excess or worn out organelles, food particles, and engulfed viruses or bacteria. The typically originate from the golgi apparatus.

nuclear envelope

The nuclear envelope surrounds the nucleus with a double membrane with multiple pores. The pores regulate the passage of macromolecules like proteins and RNA, but permit free passage of water, ions, ATP and other small molecules.

nucleus Known as the cell’s “command center,” the nucleus is a large organelle that stores the cell’s DNA (deoxyribonucleic acid). The nucleus controls all of the cell’s activities, such as growth and metabolism, using the DNA’s genetic information.

nucleolus The nucleolus is a round body located inside the nucleus of a eukaryotic cell. It is not surrounded by a membrane but sits in the nucleus. The nucleolus makes ribosomal subunits from proteins and ribosomal RNA, also known as rRNA. It then sends the subunits out to the rest of the cell where they combine into complete ribosomes.

chromosomes Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of a single molecule of deoxyribonucleic acid (DNA) and proteins. Chromosomes usually appear during cell division when chromatin coils up. Chromosomes are then divided evenly to create two new cells during cell division.

A2. identify the functional interrelationships of cell structures

You need to be able to describe how 2 (or more) cell organelles work together to accomplish a function.

Examples:

(1) Protein Production – nucleus, ribosomes/rough ER(2) Protein Secretion – Rough ER, Golgi, Secretory Vesicle, Cell Membrane(3) Cellular digestion – vacuole and lysosome(4) Ion Transport – Mitochondria/ATP and Sodium/Potassium pump

A3. identify the cell structures in diagrams and electron micrographs

Part Functioncell membrane

mitochondria

Smooth & Rough endoplasmic reticulum

ribosomes

Golgi bodies

vesiclesSee Golgi picture above

vacuoles

lysosomes

nuclear envelope

See nucleus picture below

nucleus

nucleolus See nucleus picture above.

chromosomes

Cell Processes and Applications (Transport Across Cell Membrane)

It is expected that students will:

G1. apply knowledge of organic molecules to explain the structure and function of the fluid-mosaic membrane model

Fluid Mosaic Model: The plasma membrane is a fluid combination of phospholipids, cholesterol, and proteins. The 'Fluid' part represents how some parts of the membrane can move around freely, if they are not attached to other parts of the cell. The “Mosaic” part represents how various molecules (i.e. proteins) are scattered throughout the lipid bilayer.

Carbohydrates attached to lipids (glycolipids) and to proteins (glycoproteins) extend from the outward-facing surface of the membrane.

G2. explain why the cell membrane is described as "selectively permeable"

A selectively permeable cell membrane is one that allows certain molecules or ions to pass through it by means of active or passive transport.

Generally:

(a) small/non-polar molecules freely pass through the cell membrane (ex: O2, CO2, steroids, alcohols)(b) small/polar molecules travel through transport proteins (channels or pumps) to cross the cell

Membrane (ex. glucose, amino acids with polar remainder groups, water).(c) large molecules (or cells) pass through membrane via endo/exocytosis

G3. compare and contrast the following: diffusion, facilitated transport, osmosis, active transport

Type Definition

Passive Transport(no energy required, movement is caused

by difference in concentration gradient)

Diffusion● movement of solute from area of high concentration to area of low concentration● usually occurs directly through cell membranes

Osmosis

● movement of water (solvent) from area of high water concentration to area of low water concentration (or, movement of water from area of low solute concentration to area of high solute concentration

Facilitated Diffusion

● movement of solute, through a transport protein, from area of high concentration to area of low concentration, across a cell membrane

Active Transport(required energy,

usually ATP)

Active Transport (pumps)

● movement of molecules from area of low concentration to area of high concentration (‘against’ the concentration gradient).

Endocytosis ● process where cell membrane folds to capture large molecules, or cells, and bring them inside the cell via a vacuole (see outcome G5 for more info)

Exocytosis● process where a vacuole fuses with the cell membrane to release the vacuole contents to the outside of the cell (see outcome G5 for more info)

G4. explain factors that affect the rate of diffusion across a cell membrane

(a) Concentration Gradient – greater difference in concentration leads to a higher ‘motivation’ for molecules to move to the area of low concentration

(b) Temperature – increased temperature leads to more kinetic energy of molecules. This increased movement helps molecules ‘spread out’ faster, and also increases the chance that a molecule will ‘find’ spaces in a cell membrane to move through.

(c) Surface Area – more surface area provides more ‘spaces’ or ‘gates’ for molecules to pass through the cell membrane.

(d) Type of molecule – small/non-polar molecules are more likely to pass through the small spaces between phospholipids in a cell membrane

(e) Distance – diffusion rates are increased when the distance is decreased. For example, the time it takes molecules to reach the middle of small cell will be lower than the time needed for molecules to reach the middle of a large cell (ex. agar cell lab).

G5. describe endocytosis, including phagocytosis and pinocytosis, and contrast it with exocytosis

All involve the movement of large molecules, such as proteins or entire cells.All are considered active transport because ATP is required for these processes to occur.

G6. predict the effects of hypertonic, isotonic, and hypotonic environments on animal cells

Hypertonic A hypertonic solution has a greater concentration of solutes than another solution. In biology, the tonicity of a solution usually refers to its solute concentration relative to that of another solution on the opposite side of a cell membrane; a solution outside of a cell is called hypertonic if it has a greater concentration of solutes than the cytosol inside the cell. When a cell is immersed in a hypertonic solution, osmotic pressure tends to force water to flow out of the cell in order to balance the concentrations of the solutes on either side of the cell membrane. The cytosol is conversely categorized as hypotonic, opposite of the outer solution.

Hypotonic A hypotonic solution has a lower concentration of solutes than another solution. In biology, a solution outside of a cell is called hypotonic if it has a lower concentration of solutes relative to the cytosol. Due to osmotic pressure, water diffuses into the cell, and the cell often appears turgid, or bloated. For cells without a cell wall such as animal cells, if the gradient is large enough, the uptake of excess water can produce enough pressure to induce cytolysis, or rupturing of the cell. When plant cells are in a hypotonic solution, the central vacuole takes on extra water and pushes the cell membrane against the cell wall. Due to the rigidity of the cell wall, it pushes back, preventing the cell from bursting. This is called turgor pressure.

Isotonic A solution is isotonic when its effective osmole concentration is the same as that of another solution. In biology, the solutions on either side of a cell membrane are isotonic if the concentration of solutes outside the cell is equal to the concentration of solutes inside the cell. In this case the cell neither swells nor shrinks because there is no concentration gradient to induce the diffusion of large amounts of water across the cell membrane. Water molecules freely diffuse through the plasma membrane in both directions, and as the rate of water diffusion is the same in each direction, the cell will neither gain nor lose water.

Example: Human Blood Cells

G7. demonstrate an understanding of the relationship and significance of surface area to volume, with reference to cell size

Surface area to the volume ratio (SA:V) gets smaller as a cell gets larger. Thus, if the cell grows beyond a certain limit, not enough material will be able to cross the membrane fast enough (“supply”) to accommodate the increased cellular volume and activities (“demand”)