Plant and animal cells have many of the same structures.
But plants have a few specialized
structures for support and to make food.TRINSET/ISTOCK/GETTY IMAGES PLUS;
ADAPTED BY L. STEENBLIK HWANG
Key features of cells from multi-celled organisms include:
a nucleus. The nucleus is a protective membrane surrounding a cell’s
DNA. It keeps this genetic “instruction manual” safe from molecules
that could damage it. The presence of a nucleus is what makes a
eukaryotic cell different from a prokaryotic one.
endoplasmic reticulum (En-doh-PLAZ-mik Reh-TIK-yoo-lum). This place,
where a cell makes proteins and fats, has a long name. But you can
call it “ER” for short. It’s a flat sheet that gets folded tightly back and
forth. Those known as rough ERs makes proteins. The ribosomes that
attach to this ER give it that “rough” appearance. Smooth ERs make
not only lipids (fatty compounds such as oils, waxes, hormones and
most parts of the cell membrane) but also cholesterol (a waxy material
in plants and animals). Those proteins and other materials become
packaged into tiny sacs that pinch off from the edge of the ER. These
important products of cells are then transported to the Golgi (GOAL-
jee) apparatus.
Golgi apparatus. This organelle modifies proteins and lipids in much the
same way auto parts are added to the body of a car in the factory’s
assembly line. For example, some proteins need carbohydrates
attached to them. After these additions are made, the Golgi apparatus
packages up the modified proteins and lipids, then ships them in sacs
known as vesicles to where they will be needed in the body. It’s like a
post office that receives lots of mail for different people. The Golgi
apparatus sorts the cellular “mail” and delivers it to the proper body
address.
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cytoskeleton. This network of tiny fibers and filaments provides structure
to a cell. It’s like the frame of a house. Different cells have different
shapes and structures based on their function. For example, a muscle
cell has a long, cylindrical structure so that it can contract.
mitochondria. These power generators of the cell break down sugars to
release their energy. Then the mitochondria (My-toh-KON-dree-uh)
package that energy into a molecule called ATP. It’s the form of
energy that cells use to power their activities.
lysosomes. These organelles are the cell’s recycling centers. They break
down and digest nutrients, waste or old parts of the cell that are no
longer needed. If a cell is too damaged to repair, lysosomes help the
cell destroy itself by breaking down and digesting all the structural
supports as well. That type of cell suicide is known as apoptosis.
vacuoles. In animal cells, several of these small sac-like structures work
a bit like lysosomes, helping to recycle wastes. In plant cells, there is
one large vacuole. It mainly stores water and keeps a cell hydrated,
which helps give a plant its rigid structure.
Viewed here under a microscope, chloroplasts are the structures in plant cells that make plants
green.NNEHRING/E+/GETTY IMAGES PLUS
cell wall. This rigid layer jackets the outside of a plant’s cell membrane.
It’s made of a network of proteins and sugars. It gives plants their stiff
structure and provides some protection from pathogens and from
stress, such as water loss.
chloroplasts. These plant organelles use energy from the sun, along with
water and carbon dioxide in the air, to make food for plants through
the process known as photosynthesis. Chloroplasts (KLOR-oh-plasts)
have a green pigment inside them called chlorophyll. This pigment is
what makes plants green.
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amino acids: Simple molecules that occur naturally in plant and animal tissues and that are the
basic building blocks of proteins.
amoeba: A single-celled microbe that catches food and moves about by extending fingerlike
projections of a colorless material called protoplasm. Amoebas are either free-living in damp
environments or they are parasites.
ATP: Short for adenosine triphosphate. Cells make this molecule to power almost all of their
activities. Cells use oxygen and simple sugars to create this molecule, the main source of their
energy. The small structures in cells that carry out this energy-storing process are known as
mitochondria. Like a battery, ATP stores a bit of usable energy. Once the cell uses it up,
mitochondria must recharge the cell by making more ATP using energy harvested from the cell’s
nutrients.
bacteria: (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on
Earth, from the bottom of the sea to inside other living organisms (such as plants and
animals). Bacteria are one of the three domains of life on Earth.
biologist: A scientist involved in the study of living things.
carbohydrates: Any of a large group of compounds occurring in foods and living tissues,
including sugars, starch and cellulose. They contain hydrogen and oxygen in the same ratio as
water (2:1) and typically can be broken down in an animal’s body to release energy.
carbon dioxide: (or CO2) A colorless, odorless gas produced by all animals when the oxygen
they inhale reacts with the carbon-rich foods that they’ve eaten. Plants convert carbon dioxide
into oxygen during photosynthesis, the process they use to make their own food.
cell: (in biology) The smallest structural and functional unit of an organism.
cell membrane: A structure that separates the inside of a cell from what is outside of it. Some
particles are permitted to pass through the membrane.
chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion
and structure. For example, water is a chemical made when two hydrogen atoms bond to one
oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe
properties of materials that are the result of various reactions between different compounds.
chlorophyll: Any of several green pigments found in plants that perform photosynthesis —
creating sugars (foods) from carbon dioxide and water.
chloroplast: A tiny structure in the cells of green algae and green plants that contain chlorophyll
and creates glucose through photosynthesis.
cholesterol: A fatty material in animals that forms a part of cell walls. In vertebrate animals, it
travels through the blood in little vessels known as lipoproteins. Excessive levels in the blood
can signal risks to blood vessels and heart.
contract: To activate muscle by allowing filaments in the muscle cells to connect. The muscle
becomes more rigid as a result.
develop: To emerge or to make come into being, either naturally or through human intervention,
such as by manufacturing. (in biology) To grow as an organism from conception through
adulthood, often undergoing changes in chemistry, size, mental maturity or sometimes even
shape.
digest: (noun: digestion) To break down food into simple compounds that the body can absorb
and use for growth. Some sewage-treatment plants harness microbes to digest — or degrade —
wastes so that the breakdown products can be recycled for use elsewhere in the environment.
DNA: (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule
inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus,
oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these
instructions tell cells which molecules to make.
environment: The sum of all of the things that exist around some organism or the process and
the condition those things create. Environment may refer to the weather and ecosystem in which
some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in
the vicinity of an item of interest).
eukaryote: Any organism whose cells have a nucleus. Eukaryotes include all multicellular
creatures (such as plants, animals and fungi) as well as certain types of single-celled
microorganisms.
fat: A natural oily or greasy substance occurring in plants and in animal bodies, especially when
deposited as a layer under the skin or around certain organs. Fat’s primary role is as an energy
reserve. Fat also is a vital nutrient, though it can be harmful if consumed in excessive amounts.
fiber: Something whose shape resembles a thread or filament. (in nutrition) Components of
many fibrous plant-based foods. These so-called non-digestible fibers tend to come from
cellulose, lignin, and pectin — all plant constituents that resist breakdown by the body’s
digestive enzymes.
filament: Something with a thin, thread-like shape. For instance, the fragile metal wire that heats
up to emit light inside an incandescent light bulb is known as its filament.
fungi: (sing: fungus) Organisms with one or more cells that reproduce via spores and feed on
living or decaying organic matter. Examples include mold, yeasts and mushrooms.
genetic: Having to do with chromosomes, DNA and the genes contained within DNA. The field
of science dealing with these biological instructions is known as genetics. People who work in
this field are geneticists.
liver: An organ of the body of animals with backbones that performs a number of important
functions. It can store fat and sugar as energy, break down harmful substances for excretion by
the body, and secrete bile, a greenish fluid released into the gut, where it helps digest fats and
neutralize acids.
lysosome: A major structure within cells that is surrounded by a membrane. It's interior liquid is
acidic and contains enzymes that can be used to break down (digest) proteins and other types of
molecular trash — materials for which the cell no longer has any need
membrane: A barrier which blocks the passage (or flow through) of some materials depending
on their size or other features. Membranes are an integral part of filtration systems. Many serve
that same function as the outer covering of cells or organs of a body.
messenger RNA: A type of genetic material that is copied from DNA. This mRNA carries the
instructions for building a cell’s proteins.
microscope: An instrument used to view objects, like bacteria, or the single cells of plants or
animals, that are too small to be visible to the unaided eye.
mitochondria: (sing. mitochondrion) Structures in all cells (except bacteria and archaea) that
break down nutrients, converting them into a form of energy known as ATP.
molecule: An electrically neutral group of atoms that represents the smallest possible amount of
a chemical compound. Molecules can be made of single types of atoms or of different types. For
example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two
hydrogen atoms and one oxygen atom (H2O).
multicellular: Having or consisting of many cells. This includes all animals and plants, and
many types of fungus.
muscle: A type of tissue used to produce movement by contracting its cells, known as muscle
fibers. Muscle is rich in protein, which is why predatory species seek prey containing lots of this
tissue.
network: A group of interconnected people or things. (v.) The act of connecting with other
people who work in a given area or do similar thing (such as artists, business leaders or medical-
support groups), often by going to gatherings where such people would be expected, and then
chatting them up.
nitrogen: A colorless, odorless and nonreactive gaseous element that forms about 78 percent of
Earth's atmosphere.
nucleotides: The four chemicals that, like rungs on a ladder, link up the two strands that make up
DNA. They are: A (adenine), T (thymine), C (cytosine) and G (guanine). A links with T, and C
links with G, to form DNA. In RNA, uracil takes the place of thymine.
nucleus: Plural is nuclei. (in biology) A dense structure present in many cells. Typically a single
rounded structure encased within a membrane, the nucleus contains the genetic information. (in
astronomy) The rocky body of a comet, sometimes carrying a jacket of ice or frozen gases. (in
physics) The central core of an atom, containing most of its mass.
nutrient: A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism
requires as part of its food in order to survive.
organelle: Specialized structures, such as mitochondria, found within a cell.
organism: Any living thing, from elephants and plants to bacteria and other types of single-
celled life.
oxygen: A gas that makes up about 21 percent of Earth's atmosphere. All animals and many
microorganisms need oxygen to fuel their growth (and metabolism).
pathogen: An organism that causes disease.
permeable: Having pores or openings that permit liquids or gases to pass through. Sometimes
materials can be permeable for one particular type of liquid or gas (water, for example) but block
others (such as oil)
phosphate: A chemical containing one atom of phosphorus and four atoms of oxygen. It is a
component of bones, hard white tooth enamel, and some minerals such as apatite.
photosynthesis: (verb: photosynthesize) The process by which green plants and some other
organisms use sunlight to produce foods from carbon dioxide and water.
pigment: A material, like the natural colorings in skin, that alter the light reflected off of an
object or transmitted through it. The overall color of a pigment typically depends on which
wavelengths of visible light it absorbs and which ones it reflects.
prokaryote: Any single-celled organism that does not have a nucleus or membrane-bound
organelles.
protein: A compound made from one or more long chains of amino acids. Proteins are an
essential part of all living organisms. They form the basis of living cells, muscle and tissues; they
also do the work inside of cells. Among the better-known, stand-alone proteins are
the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections.
Medicines frequently work by latching onto proteins.
range: The full extent or distribution of something. For instance, a plant or animal’s range is the
area over which it naturally exists.
recycle: To find new uses for something — or parts of something — that might otherwise be
discarded, or treated as waste.
RNA: A molecule that helps “read” the genetic information contained in DNA. A cell’s
molecular machinery reads DNA to create RNA, and then reads RNA to create proteins.
stress: (in biology) A factor — such as unusual temperatures, movements, moisture or pollution
— that affects the health of a species or ecosystem.
trillion: A number representing a million million — or 1,000,000,000,000 — of something.
unicellular: An adjective for organisms that possess a single cell, such as an amoeba or
bacterium.
unique: Something that is unlike anything else; the only one of its kind.
unit: (in measurements) A unit of measurement is a standard way of expressing a physical
quantity. Units of measure provide context for what numerical values represent and so convey
the magnitude of physical properties. Examples include inches, kilograms, ohms, gauss, decibels,
kelvins and nanoseconds.
vesicle: A small fluid-filled sac inside cells. These sacs can hold chemicals that can be released
either within the cell or outside of it.
