Biology Questions and Answers –
Cell Biology Essentials |
Comprehensive Review of Cell
Structure and Function (2025
Edition)
Biology Questions and Answers
(DNA or RNA) enwrapped by a protein
Cell Structure capsule. They do not have membranes
and cell organelles nor do they have self-
metabolism.
1. What is cell theory?
Cell theory asserts that the cell is the
constituent unit of living beings.
Before the discovery of the cell, it was
not recognized that living beings were
made of building blocks like cells.
The cell theory is one of the basic
theories of Biology.
2. Are there living beings
without cells?
Viruses are considered the only living
beings that do not have cells. Viruses
are constituted by genetic material
,3. In 1665 Robert Hooke,
an English scientist,
published his book
Micrographia, in which he
described that pieces of
cork viewed under the
microscope presented small
cavities similar to pores
which were filled with air.
Based on later knowledge,
of what were the walls of
those cavities constituted?
What is the historical
importance of that
observation?
The walls of the cavities observed
by Hooke were the walls of the
plant cells that form the tissue. The
observation led to the discovery of
the cells, a fact only possible after
the invention of the microscope. In
that work, Hooke established the
term “cell”, now widely used in
Biology, to designate those cavities
seen under the microscope.
4. What are the two big
groups into which cells
are classified?
Cells can be classified as eukaryotic
or prokaryotic.
Prokaryotic cell is that without a
delimited nucleus. Eukaryotic cells
are those with nucleus delimited by
membrane.
, Biology Questions and Answers
5. Do bacteria cells have a pointing to the exterior of the layer and
nucleus? the non-polar phospholipid chains in the
interior. Proteins can be found
embedded in the lipid bilayer and there
In bacteria the genetic material is
are also some carbohydrates bound to
dispersed in the cytosol and there is no proteins and to phospholipids in the
internal membrane that delimits a outer face of the membrane.
nucleus.
9. What is the difference
6. Are there any bacteria
between plasma membrane
made of more than one cell?
and cell wall?
There are no pluricellular bacteria. All
bacteria are unicellular prokaryotic. Plasma membrane and cell wall are not
the same thing. Plasma membrane, also
called cell membrane, is the outer
membrane common to all living cells
and it is made of a phospholipid bilayer,
7. What is the plasma
embedded proteins and some appended
membrane of the cell? What carbohydrates.
are its main functions?
Because cell membranes are fragile, in
The plasma membrane is the outer some types of cells there are even outer
membrane of the cell, it delimits the cell structures that support and protect the
itself and a cell interior with specific membrane, like the cellulose wall of
conditions for the cellular function. plant cells and the chitin wall of some
Since it is selectively permeable, the fungi cells. Most bacteria also present
plasma membrane has an important an outer cell wall made of
role for the passage of substances peptidoglycans and other organic
inwards or outwards. substances.
8. What are the chemical 10. What are the main
substances that compose the respective constituents of cell
plasma membrane? walls in bacteria, protists,
fungi and plants?
The main constituents of the plasma
membrane are phospholipids, proteins In bacteria the cell wall is made of
and carbohydrates. The phospholipds, peptidoglycans; among protists algae
amphipathic molecules, are regularly have cell walls made of cellulose; in
organized in the membrane according to fungi, the cell wall is made of chitin (the
their polarity: two layers of same substance that makes the
phospholipids form the lipid bilayer with
the polar part of the phospholipids
, Biology Questions and Answers
exoskeleton of arthropods); in plants, and thus they are eukaryotic cells; in
the cell wall is made of cellulose too. these cells the genetic material is
located within the nucleus. Bacterial
cells (cells of living beings of the
kingdom Monera) do not have organized
11. Do membranes form only cellular nuclei and so they are
the outer wrapping of cells? prokaryotic cells and their genetic
material is found dispersed in the
cytosol.
Lipid membranes do not form only the
outer cover of cells. Cell organelles,
such as the Golgi complex,
mitochondria, chloroplasts, lysosomes,
the endoplasmic reticula and the
14. What are the three main
nucleus, are delimited by membranes parts of a eukaryotic cell?
too.
The eukaryotic cell can be divided into
two main portions: the cell membrane
that separates the intracellular space
12. Which type of cell came from the outer space physically
first in evolution - the delimiting the cell; the cytoplasm, the
eukaryotic cell or the interior portion filled with cytosol (the
aqueous fluid inside the cell); and the
prokaryotic cell? nucleus, the membrane-delimited
internal region that contains the genetic
This is an interesting problem of material.
biological evolution. The most accepted
hypothesis asserts that the more simple
cell, the prokaryotic cell, appeared
earlier in evolution than the more 15. What are the main
complex eukaryotic cell. The structures within the cell
endosymbiotic hypothesis, for example,
affirms that aerobic eukaryotic cells
nucleus?
appeared from the mutualist ecological
interaction between aerobic prokaryotes Within the cell nucleus the main
and primitive anaerobic eukaryotes. structures are: the nucleolus, an
optically dense region, spherical shaped,
where there are concentrated ribosomal
RNA (rRNA) associated to proteins
13. Concerning the presence (there may be more than one nucleolus
of the nucleus what is the in a nucleus); the chromatin, made of
DNA molecules dispersed in the nuclear
difference between animal matrix during the cell interphase; the
and bacterial cells? karyotecha, or nuclear membrane, the
membrane that delimits the nucleus.
Animal cells (cells of living beings of the
kingdom Animalia) have an interior
membrane that delimits a cell nucleus
Cell Biology Essentials |
Comprehensive Review of Cell
Structure and Function (2025
Edition)
Biology Questions and Answers
(DNA or RNA) enwrapped by a protein
Cell Structure capsule. They do not have membranes
and cell organelles nor do they have self-
metabolism.
1. What is cell theory?
Cell theory asserts that the cell is the
constituent unit of living beings.
Before the discovery of the cell, it was
not recognized that living beings were
made of building blocks like cells.
The cell theory is one of the basic
theories of Biology.
2. Are there living beings
without cells?
Viruses are considered the only living
beings that do not have cells. Viruses
are constituted by genetic material
,3. In 1665 Robert Hooke,
an English scientist,
published his book
Micrographia, in which he
described that pieces of
cork viewed under the
microscope presented small
cavities similar to pores
which were filled with air.
Based on later knowledge,
of what were the walls of
those cavities constituted?
What is the historical
importance of that
observation?
The walls of the cavities observed
by Hooke were the walls of the
plant cells that form the tissue. The
observation led to the discovery of
the cells, a fact only possible after
the invention of the microscope. In
that work, Hooke established the
term “cell”, now widely used in
Biology, to designate those cavities
seen under the microscope.
4. What are the two big
groups into which cells
are classified?
Cells can be classified as eukaryotic
or prokaryotic.
Prokaryotic cell is that without a
delimited nucleus. Eukaryotic cells
are those with nucleus delimited by
membrane.
, Biology Questions and Answers
5. Do bacteria cells have a pointing to the exterior of the layer and
nucleus? the non-polar phospholipid chains in the
interior. Proteins can be found
embedded in the lipid bilayer and there
In bacteria the genetic material is
are also some carbohydrates bound to
dispersed in the cytosol and there is no proteins and to phospholipids in the
internal membrane that delimits a outer face of the membrane.
nucleus.
9. What is the difference
6. Are there any bacteria
between plasma membrane
made of more than one cell?
and cell wall?
There are no pluricellular bacteria. All
bacteria are unicellular prokaryotic. Plasma membrane and cell wall are not
the same thing. Plasma membrane, also
called cell membrane, is the outer
membrane common to all living cells
and it is made of a phospholipid bilayer,
7. What is the plasma
embedded proteins and some appended
membrane of the cell? What carbohydrates.
are its main functions?
Because cell membranes are fragile, in
The plasma membrane is the outer some types of cells there are even outer
membrane of the cell, it delimits the cell structures that support and protect the
itself and a cell interior with specific membrane, like the cellulose wall of
conditions for the cellular function. plant cells and the chitin wall of some
Since it is selectively permeable, the fungi cells. Most bacteria also present
plasma membrane has an important an outer cell wall made of
role for the passage of substances peptidoglycans and other organic
inwards or outwards. substances.
8. What are the chemical 10. What are the main
substances that compose the respective constituents of cell
plasma membrane? walls in bacteria, protists,
fungi and plants?
The main constituents of the plasma
membrane are phospholipids, proteins In bacteria the cell wall is made of
and carbohydrates. The phospholipds, peptidoglycans; among protists algae
amphipathic molecules, are regularly have cell walls made of cellulose; in
organized in the membrane according to fungi, the cell wall is made of chitin (the
their polarity: two layers of same substance that makes the
phospholipids form the lipid bilayer with
the polar part of the phospholipids
, Biology Questions and Answers
exoskeleton of arthropods); in plants, and thus they are eukaryotic cells; in
the cell wall is made of cellulose too. these cells the genetic material is
located within the nucleus. Bacterial
cells (cells of living beings of the
kingdom Monera) do not have organized
11. Do membranes form only cellular nuclei and so they are
the outer wrapping of cells? prokaryotic cells and their genetic
material is found dispersed in the
cytosol.
Lipid membranes do not form only the
outer cover of cells. Cell organelles,
such as the Golgi complex,
mitochondria, chloroplasts, lysosomes,
the endoplasmic reticula and the
14. What are the three main
nucleus, are delimited by membranes parts of a eukaryotic cell?
too.
The eukaryotic cell can be divided into
two main portions: the cell membrane
that separates the intracellular space
12. Which type of cell came from the outer space physically
first in evolution - the delimiting the cell; the cytoplasm, the
eukaryotic cell or the interior portion filled with cytosol (the
aqueous fluid inside the cell); and the
prokaryotic cell? nucleus, the membrane-delimited
internal region that contains the genetic
This is an interesting problem of material.
biological evolution. The most accepted
hypothesis asserts that the more simple
cell, the prokaryotic cell, appeared
earlier in evolution than the more 15. What are the main
complex eukaryotic cell. The structures within the cell
endosymbiotic hypothesis, for example,
affirms that aerobic eukaryotic cells
nucleus?
appeared from the mutualist ecological
interaction between aerobic prokaryotes Within the cell nucleus the main
and primitive anaerobic eukaryotes. structures are: the nucleolus, an
optically dense region, spherical shaped,
where there are concentrated ribosomal
RNA (rRNA) associated to proteins
13. Concerning the presence (there may be more than one nucleolus
of the nucleus what is the in a nucleus); the chromatin, made of
DNA molecules dispersed in the nuclear
difference between animal matrix during the cell interphase; the
and bacterial cells? karyotecha, or nuclear membrane, the
membrane that delimits the nucleus.
Animal cells (cells of living beings of the
kingdom Animalia) have an interior
membrane that delimits a cell nucleus
