Chapter 2: The Cell: Life’s Basic Building Block Summary

The plasma membrane

The plasma membrane positions the cell cytoplasm in place.

It allows substances to leave or enter into the cell.

The nature of the semi permeability of the plasma membrane is because of the phospholipid bilayer with protein molecules interspersed in it.

The outer surface of the plasma membrane has hydrophilic polar heads.

The inner side of the double layer contains hydrophobic nonpolar tails derived from fatty acid chains.

Polar heads attract water molecules that are polarized by the process of electrostatic attraction.

Phospholipids have both nonpolar and polar ends hence they are referred to as amphipathic molecules.

Movement across the cell membrane

• Diffusion: This process involves the movement of molecules from a highly concentrated region to a lowly concentrated region.
  • At equilibrium, diffusion continues but at an equal flow rate in both directions.
  • The rate of diffusion depends on the temperature the size of the molecule.
  • Diffusion is one type of passive transport where energy is not required for movement to occur.
  • Facilitated diffusion involves the movement of lipid-soluble molecules across the cell membrane.
• Osmosis: This is the process through which a solvent moves from a highly concentrated region to a region of low concentration through a semipermeable membrane.
  • Polar molecules like water cannot pass through the lipid bilayer.
  • For osmosis to occur, there must be a difference in the concentration of water molecules on the two membrane sides.
  • Solute concentration in water molecules affects the rate of osmosis.
  • An isotonic solution is a solution with equal solvent and solute concentration in a cell.
  • A hypotonic solution is a solution of high water concentration and a low solute concentration.
  • A hypertonic solution has a lower water concentration and a high solute concentration.
• Active transport: This is the process by which substances move across the plasma membrane against the concentration gradient.
  • Movement from a lowly concentrated region to a highly concentrated region requires ATP energy.
  • Active transport allows cells to absorb nutrients that are not absorbed across the membrane by other means.

The nucleus

It is the biggest organelle in the cell.

It is covered by the nuclear envelope.

It contains DNA packed in chromatin networks.

Chromatin contract to form chromosomes.

The chromosomes contain DNA.

The nucleus has a nucleolus which stores molecules of RNA and generates ribosomes.

Endoplasmic reticulum

• This organelle transports materials such as RNA and protein molecules.
• It provides a site for the synthesis of proteins and lipids.
• There two types of ER:
  • Rough ER has ribosomes on the outer surface.
  • Smooth ER does not have ribosomes on its surface.

Flagellum

• It is a cytoplasmic whip-like projection found on the exterior surface of the cell.
• It is found on sperm cell cells in humans for locomotion.

Golgi apparatus

• This organelle is found near the nucleus.
• It helps in storing, modifying, and packaging of protein molecules released from secretions into various parts of the cell.

Lysosome

• It is a membranous membrane containing digestive enzymes and acids.
• It digests large food molecules like carbohydrates, nucleic acids, and proteins into simple forms important to the cell.
• It helps in the destruction of foreign molecules and the removal of nonfunctioning cell structures.

Mitochondrion

• This organelle performs cellular respiration including food oxidation and release of ATP energy into the cell.
• The ATP energy helps to accelerate chemical reactions.

Ribosomes

• Ribosomes contain 40% of proteins and 60% of RNA.
• They produce protein through the translation of RNA.

Vacuoles

• They are mostly found in plant cells.
• They carry substances to be discharged out of the cell on to the cell membrane.
• They help in isolating cellular debris from the cell.

Cilia

• They are cytoplasmic hair-like projections found on the outer surface of the cell.
• In multicellular organisms, they move materials over the cell surface.
• They are used for locomotion in unicellular organisms.

Revision

Cell Therory
The therory that all living things are composed of cells, cells are the basic units of structure & function in living things, and new cells are produced from existing cells.

Schwann
This Scientist worked with animals.

Prokaryote
A unicellular organism lacking a nucleus.

Eukaryote
An organism whose cells contain nuclei.

Nucleus
The center of the atom which contains the protons and neutrons; in cells, structure that contains the cell’s genetic material (DNA) and controls the cell’s activities.

Organelles
A specialized structure that performs important cellular functions within a eukaryotic cell.

Cytoplasm
A material inside the cell membrane-not including the nucleus.

Nuclear Envelope
A layer of two membranes that surrounds the nucleus of a cell.

Chromatin
A granular material visible within the nucleus; consists of DNA tigtly coiled around proteins.

Chromosome
A threadlike structure within the nucleus containing the genetuc information that is passed from one generation of cells to the next.

Nucleous
A small, dense region within most nuclei in which the assembly of proteins begins up.

Cell Wall
A strong supporting layer around the cell membrane in plants, algae, and some backteria

Cell Membrane
Helps regulate what enters and leaves the cell and also provides protection and support.

Schleiden
Works with plants and discovered that plants were also made of cells, and his theory helped lead other scientists to develop the cell theory.

Ribosomes
Helps to produce proteins by following coded instructions that come from the nucleus.

Smooth ER
This contains collections of enzymes that preform spcialized tasks, including the synthesis of membrane lipids and detoxification of drugs.

Rough ER
Is involved in the systhesis of protein, also ribosomes are found on this.

Golgi Apparatus
It modifys, sorts, and package proteins and other materials from the ER for storage in the cell or secerion outside the cell.

Lysosome
It breaksdown lipids, carbs, and proteins into small molecules that can be used by the rest of the cell.

Vacuole
It stores materials such as water, salts, proteins, and carbs.

Mitrochondrian
It converts the chemical energy stored in food into compunds that are more convienent for the cell to use.

Chloroplasts
It captures the energy from sunlight and converts it into chemical energy in a process called photosynthesis.

Cytoskeleton
It is the network of protein filaments that help the cell maintain its shape and move.

Centriole
They help organize cell division.

Hooke
Used the first light microscope to look at a slice of cork, he saw small chambers of space which he called cells.

Leeuwenhoek
He crafted the first microscope to produce magnified images of small objects.

Cytology
From the Greek word cyto, which means “cell,” is the study of cells.

Eukaryotes
Eukaryotic cells have a defined nucleus that controls and directs the cell’s activities.

Cytosol
Fluid material found in the cytoplasm that fills most of the cell.

Plasma membrane
Animal cells semipermeable cell membrane.

Hydrophobic
Water fearing

Hydrophilic
Water loving

Diffusion
Is a natural phenomenon with observable effects. Molecules or other particles spontaneously spread, or migrate, from areas of higher concentration to areas of lower concentration until equilibrium occurs. Is one form of passive transport that doesn’t require the expenditure of cellular energy.

Osmosis
Is a form of passive transport that’s similar to diffusion and involves a solvent moving through a selectively permeable or semipermeable membrane from an area of higher concentration to an area of lower concentration. Solutions are composed of two parts: a solvent and solute.

Solvent
Is the liquid in which a substance is dissolved, such as water.

Solute
Is the substance dissolved in the solvent.

Isotonic
Is a solution that has the same concentration of solute and solvent as found inside a cell. So if you place a cell in this solution, it will experience equal flow of water into and out of the cell, maintaining equilibrium.

Hypotonic
Is a solution that has less solute and higher water potential than inside the cell. Therefore, if a human cell is placed in this solution, molecules diffuse down the concentration gradient until the cell’s membrane bursts.

Hypertonic
Is a solution that has more solute and lower water potential inside the cell. If a human cell is placed in this solution, it would let water flow out of the cell (from the higher concentration inside to the lower concentration outside), therefore shrinking the cell.

Active transport
Occurs across a semipermeable membrane against the normal concentration gradient, moving from the area of lower concentration to the area of higher concentration and requiring an expenditure of energy released from an ATP molecule.

Nucleus
Is the largest cellular organelle.

Nuclear envelope
Is composed of a double membrane barrier, each membrane of which is made up of a phospholipid bilayer.

Nucleolus
The only cellular organelle found within the nucleus is called? Assembles ribosomes.

Cytoskeleton
A network of fibrous proteins inside the cytoplasm.

Microfilaments
Rod like structures about 5 to 8 nanometers wide that consist of a stacked protein called actin.

Intermediate filaments
The strongest and most stable part of the cytoskeleton. They average abut 10 nanometers wide and consist of interlocking proteins, including keratin.

Microtubules
Are about 25 nanometers in diameter and 25 to 50 Microns long made of the protein tubulin.

Organelles
Means “little organs” are nestled inside the cytoplasm.

Centrosome
An organelle that has microtubules sprout from it and is located next to the nucleus and is composed of two centrioles.

Cilia
An organelle that is short, hair like cytoplasmic projections on the external surface of the cell.

Endoplasmic reticulum
This organelle makes direct contact with the cell nucleus and functions in the transport of materials such as proteins and RNA molecules.

Rough ER
An organelle that is dotted with ribosomes on the outer surface.

Smooth ER
An organelle that has no ribosomes on the surface.

Flagellum
An organelle that is a whip like cytoplasmic projection that lies on the cell’s exterior surface. It is used for locomotion.

Golgi apparatus
This organelle consists of a stack of flattened sacs with membranes. Transport vesicles connect it with the ER.

Lysosome
A tiny membranous sac containing acids and digestive enzymes. It breaks down large food molecules into materials that the cell can use. It destroys foreign particles and helps remove nonfunctioning structures from the cell.

Mitochondrion
Called the powerhouse of the cell, this usually rod-shaped organelle consists of two membranes – a smooth outer membrane and a inner membrane that divides the organelle into compartments.

Ribosomes
These roughly 25 nanometer structures may be found along the ER or floating free in the cytoplasm.

Vacuoles
More commonly found in plant cells, these open spaces in the cytoplasm sometimes carry materials to the cell membrane for discharges to the outside of the cell. In animal cells, food vacuoles are membranous sacs formed when food masses are pinched off from the cell membrane and passed into the cytoplasm of the cell.

Endocytosis
From the Greek word meaning “within the cell,” requires energy to move large masses of material into the cell.

Exocytosis
Is an energy consuming process during which a cell directs the contents of secretory vesicles out of the cell membrane.

Proteins
FRom the Greek term, “proteios, meaning “holding first place.” Are essentially building blocks for all living systems. Are chains of amino acids.

Cell life cycle
Begins with one cell division to the beginning of the next division.

The lipid bilayer structure of the cell membrane is made possible because phospholipid
molecules contain two distinct regions:
hydrophilic, hydrophobic

region is attracted to water
hydrophilic

region is repelled by water
hydrophobic

Because it has both polar and nonpolar regions, a phospholipid is classified as a(n)
amphipathic

The movement of water molecules through a semipermeable membrane is known as
osmosis

A solution having a greater concentration of water than exists in the cell is said to be
hypotonic

Injecting a large quantity of distilled water into a human’s veins would cause many red blood cells to
swell and burst

The cell membrane does not function
in the production of energy.

The only cellular organelle found within the nucleus is called a(n)
nucleolus

DNA is packaged within
chromosomes

The nucleolus
assembles ribosomes.

This cigar-shaped organelle produces energy through aerobic respiration.
Mitochondrion.

The most abundant protein in human cells is
actin.

Which organelle gets to take out the cellular trash?
Vacuole

The very small organelle responsible for protein synthesis (making proteins) is the
ribosome.

Which organelle has ribosomes attached to it?
Rough endoplasmic reticulum.

Which organelle contains secretory materials?
Golgi apparatus.

Which of the following can change the consistency of cytoplasm?
Changes in acidity or alkalinity, Temperature, Pressure

Structures found inside the nucleus include the
chromatin network.

Long, whip-like organelle for locomotion
Flagellum:

Fluid-like interior of the cell that may become a semisolid, or colloid
Cytoplasm:

Membranous sacs containing digestive enzymes
Lysosomes:

Powerhouse of the cell
Mitochondrion:

Stores RNA in the nucleus
Nucleolus:

The word “protein” can refer to
Hormones Enzymes Antibodies

Which of the following comes first in the protein-synthesis process?
Transcription.

tRNA is used to gather
amino acids.

codon is a sequence of three
nucleotides.

Human cells can live
hours, days, Indefinitely

The cell cycle is measured
from the beginning of one cell division to the beginning of
the next.