This document outlines different levels of organization in living things from the subatomic to the ecosystem level. It begins with abiotic levels including the subatomic, atomic, and molecular levels. The biotic levels include the cellular, tissue, organ, organ system, organism, population, and ecosystem levels. At the cellular level, cells are the basic units of structure and function and can be prokaryotic or eukaryotic. Tissues are made of groups of cells working together, and organs are made of tissues that work together to carry out a specific function. Organ systems are groups of organs that work together to perform major functions in an organism.

1. LEVELS OF ORGANISATION.
Living things are complex. For that reason we define different levels of
complexivity = levels of organization.
And because all living things have a chemical base, we find the abiotic level.
ABIOTIC LEVELS (No life, inert matter)
Subatomic level: protons (+), neutrons, electrons (-)
Atomic level: Chemical elements and ions, which are chemical elements
that gain or lose electrons.
If they gain electrons they became negative. Ex: FIf they lose electrons they became positive. Ex: Ca2+
Molecular level: If they formed part of living things they are called
Biomolecules.
Biomolecules can be:
o Inorganic: If they don´t contain complex carbon. These types
of molecules can also appear in no living things.
Water.
Mineral salts.
o Organic: If they contain complex structures with carbon and
they are only find in living things. There’re 4 types:
Glucids.
Lipids.
Proteins.
Nucleic acids.
BIOTIC LEVELS (In this levels components are alive)
Cellular level: It is formed by cells and the study of them is called
cytology. Cells are the smallest units of life that can carry out the 3 living
functions by itself. They’re structural and physiological units.
There’re two types of cells and the study of the types of cells is
called Microbiology.
 Prokaryotic: Cells with no nucleus. DNA is dispersed in
the cytoplasm. Ex: Bacteria.
 Eukaryotic: Cells that have DNA inside a nucleus.
There are two types of eukaryotic cells:
Plant cells: That have a cell wall and chloroplasts.
Animal cells: That doesn’t have a cell wall and
chloroplasts
Thanks to the cellular level we can classify living things into:
o Unicellular living things, with just one cell.
o Pluricellular living things, with a lot of cells.

2. Some examples of cells:
o Red blood cells: they transport oxygen from the lungs to
the tissues. They have no nucleus for having more space
for carrying oxygen in a pigment called haemoglobin.
o Muscle cell: It contracts so that structures can be brought
closer together. They are very long and they have many
proteins in the cytoplasm.
o Ciliated cell: It has a layer of tiny hairs (cilia) which can
move and push mucus from one place to another.
o Motor nerve cell: Conducts nerve impulses. The cell has a
long fiber called an axon along through impulses travel, a
fatty sheath which gives electrical insulation and a manybranched ending which can connect with many other cells.
o Root hair cell: Absorbs minerals and water from the soil
water. The cell has a long extension which increases the
surface area for the absorption of materials.
o Xylem vessel: It transports water and supports the plant.
The cell has no cytoplasm (so water can pass freely), no
end wall (so that many cells can form a continuous tube)
and walls strengthened with a waterproof substance called
lignin.
Tissue level: A set of cells of the same origin with the same function.
The part of biology that studies this level is called Histology.
Animal tissues:
o Epithelium: Lines tubes such as the gut and covers
surfaces such as the skin.
o Connective tissue: Binds and strengthens other tissues,
such as tendons.
o Blood: Transports substances around the body, and
defends against disease.
o Skeletal Tissue: Support and protects softer tissues, and
allows movement.
o Nervous tissue: sets up nerve impulses and transmits
them around the body.
o Muscle tissue: Contracts to support and move the body.
Plant tissues:
o Epidermis: Protects against water loss, and may be
involved in absorption of water and ions.
o Mesophyll: Photosynthesis.
o Parenchyma: Fills spaces between other plant tissues and
may be involved in storage, as in potato tuber.

3. o Vascular tissue: transports materials through the plant
body.
o Strengthening tissue: Support the plant.
Organ level: A set of tissues working together in the same function.
The science that studies organs is organography.
System level: Ser of organs developing a global function. Ex:
Digestive, Respiratory…
Anatomy studies the parts and physiology the function of
systems.
Organism: When the systems join together they form an organism.
Organism can be unicellular or pluricellular.
Species: 2 individuals belong to the same species when they can
reproduce and have fertile offsprings.
Population: Set of individuals of the same species living in the same
area.
Ecosystem: All the living things of different species living together in
the same habitat.
The science that studies ecosystems is ecology.
BIOMOLECULES.
Molecules are considered biomolecules if they can be present on living things.
Some large biomolecules are made up of subunits. These subunits can be split apart by a
reaction called hydrolysis that uses water but they can also be join together again by a
reaction called condensation. Biomolecules can be organic if they are only present on
living things or inorganic if they are present in both. The science which studies all types
of biomolecules is called biochemistry.
Organic biomolecules contain carbon atoms. These carbon atoms join strongly
between them so organic molecules can be large and show a wide variety of chain and
ring structures. Types of organic biomolecules:
CARBOHYDRATES:
Carbohydrates are the same as glucids. The main function of glucids is to give us
immediate energy although they can also have other functions. Although carbohydrates
gives us immediate energy we find with that for example sugar is absorbed more
quickly than starch. There are different types of glucids:
Monosaccharides: They are sweet and are found in dissolved water. They
are made of Carbon, hydrogen and water. These monosaccharides are:
o Glucose
o Fructose
o Galactose
o Ribose.

4. Disaccharides: They are formed by 2 monosaccharides and they are also
sweet and dissolved in water.
o Lactose (milk)
o Sacarose (common sugar)
Polysaccharides are formed by a lot of monosaccharides especially
glucose but they are not sweet and they cannot be dissolved in water.
o Starch (It has an energy-giving function and it’s found in plants
where it is stored in leaves and roots.
o Glycogen (It also has an energy-giving function but it is stored in
the liver and muscles of animals.) So we can say that it is only
found in animals.
o Cellulose (It has an structural function because it forms the cell
wall of plants)
o Clitin (It also has an structural function forming the exoskeleton
of arthropods)
LIPIDS:
Their main function is the storage of energy what we call reserve energy. They
have other functions such as protection and isolation or such as a structural function
making cell membranes and hormones.
The place where they are located depends on the sex. For example, men store
lipids on the stomach and women store them on the hips. This occurs because of
hormones.
A difference with Glucids is that they cannot dissolve in water although they can
dissolve in ORGANIC SOLVENTS such as formol or petrol.
The problem of lipids is that when they are used they produced compounds that
are toxic when they are in contact with water.
They have a structure formed up of a great variation of substances and their
basic unit is Glycerol + 1,2,3 fatty acids. These fatty acids can be:


Saturated: If they have one bone. They are vegetable fat and at
room temperature they are liquid such as oil.
Insaturated: If they have two or three bones. They are animal fat
and at room temperature they are solid.
PROTEINS:
They have a structural function because they are not a source of energy unless
we are on an extreme situation.

5. However proteins also have other functions:



They are antibodies such as for example immunoglobulin.
Proteins can also be hormones such as insulin.
Haemoglobin which is formed up of proteins and that transports
O2 in red blood cells.
 For making the structure of hair and nails such as keratin
 Or as biocatalyzers which serve to speed up chemical reactions in
our body.
Proteins determinate how we are so they are formed by DNA which is expressed
in RNA and which is expressed in amino acids the basic unit of proteins. A normal
protein has 200-250 amino acids and there are 20 different amino acids (aas). Some of
this amino acids are essential because are body can’t make them.
So we can say that for forming a protein the instruction arrives the cell in DNA
language which is translated to RNA language and which is translated into amino acids
like this:
ACGAAT TCC
DNA
U G C U U A A G G RNA
Lys –Ala- Gly
Amino acids.
NUCLEIC ACIDS:
Nucleic acids are formed by DNA, genetic material located in all living things in
a nucleus and by the RNA which is an intermediate diale in the synthesis of proteins.
DNA-RNA- Proteins. (Virus don’t have DNA they only have RNA)
The basic unit of Nucleic acids is nucleotides.


In DNA it has a base of nitrogen+ deoxiribose+ phosphorus.
Which is expressed with the letters A, G, C, T.
In RNA it has a base of nitrogen+ ribose+ phosphorus. Which is
expressed with the letters A, G, C, U.
INORGANIC BIOMOLECULES.
If they are present on living things and non living things. Types of inorganic
biomolecules:
WATER, it is used to:
To transport substances.
Where most chemical reactions take place.

6. To regulate internal temperature.
To give shape to cells (especially plant cells) so it helps the hydroskeleton.
Also we find that water reaches its highest density at 4 ºC. This means that ice
floats in water. These is very important for ecosystems because like that, when
winter comes and for example a lake frizzes, only its upper part frizzes and
animals can continue living in the water under the ice.
MINERAL SALTS.
If they are dissolved in liquids (water) in the form of ions, they are responsible of:
 Transmission of nervous impulse
 Muscular contraction.
 The pumping of the heart.
 Blood clotting.
If they are solid mineral salts with hard structures, they form up:



Teeth
Bones
Shells
CELLULAR LEVEL
THE CELL THEORY.
Cells were discovered by Hooke in the year 1665 thanks to the study of cork but
it was later when Brown discovered that they have a nucleus. However it was in the
year 1838 when Schleiden and Schwom developed the cell theory. It established that:
1. All living things are made up of cells.
2. Cells are the smallest functional and physiological unit of all living things which
means that cells in appropriate conditions can live by their own.
3. Every cell comes from another cell. This phrase was a revolution because it went
again the expontaneus generation which said that life could come from inert
matter.
4. Cells in pluricellular organisms can function independently although they work
together in a coordinated way.
CELL NUTRITION.
It allows cells to obtain matter (used to build new structures or to grow) and
energy (used to carry out the cellular functions).

7. We can classify cells due to nutrition into 2 types of cells:
Autotrophic cells: Those cells which have chloroplasts or pigments for
carrying out photosynthesis to turn inorganic matter into organic matter. This
is the case of plant cells, algae and some bacteria such as Cyanobacteria.
Heterotrophic cells: Are those that obtain organic matter and use it
accompanied by inorganic matter.
However we find that at the end both types of cells end with organic matter with
which the carry out metabolism that is the set of chemical reactions which take place in
the cells. It can be:
Catabolism: In which organic substances are broken down into simple ones
for releasing energy through breaking chemical lings in the form of the
molecule ATP. The best example of this is cellular respiration.
Anabolism: Instead in anabolism simple organic substances are condensed to
form complex organic substances. So we form bonds. The best example of this
is photosynthesis. However we find that for doing this process we need energy
that is given by the molecule ATP.
For metabolism it is very important transport to import and export substances but
also enzymes are very important because without them metabolism would be very slow.
There are 2 types of transport:
Passive transport: On which no energy is required. Such as for example
diffusion and osmosis.
o Diffusion: Is the type of transport mainly used by O2, CO2 and
mineral salts dissolved in water. This occurs because diffusion occurs
through partially permeable membranes which are membranes that
allow water pass through them but not big molecules. This happens for
example in Alveoli and in cells. So we can say that diffusion takes
places in fluids and from places where the concentration gradients are
high (hypertonic solutions) as in these solutions particles are close
together and so they collide with each other; to solutions where
concentration gradients are low (hypotonic solutions) and that it stops
when the gradients are equal and so the 2 solutions are equal in what
we know as Isotonic solutions. We find that for moving substances in
favor of the concentration gradient we do not need energy (high-low)
but that for going against it (low-high), yes. For diffusion we need:
 Short distances of diffusion so you need thin membranes.
 Wet surfaces
 Large surfaces of diffusion so that diffusion is higher.
 Constant concentration gradients so that the solution never
balance and diffusion continues.

8. There are 2 types of diffusion:


Simple. Molecules just pass.
Facilitated: Molecules pass thanks to the help of proteins
incrusted in the membranes. These proteins work as channels
that allow proteins to pass through them
o Osmosis: The passing of water from a high water concentration
solution or from a solution with a high water potential to a low water
concentration solution or from a low water potential; or what it is the
same from a hypotonic solution to a hypertonic solution. The
difference in height between solutions through the process of osmosis
is called pressure. Cells with partially permeable membranes need to
be in isotonic solutions as if not osmosis takes places; 2 things can
occur:
 If an animal cell is in a solution with a low water potential or
what isthe same: in a hypertonic solution; the cell releases
water shrinking and becoming crenated.

If an animal cell is in a solution with a very high water
potential such as for example in distilled water, animal cells
tend to absorb water and at the end burst.
For avoiding this our organism takes care that the plasma has the same
water potential as cells in what we call osmoregulation. In plant cells this
problem is not so big as they are protected by a cell wall. When cell
plants are in a solution that has a high water potential plant cells tend to
swell increasing a lot the size of the vacuole but they never burst as they
have the cell wall. Instead when the cell is in a low water potential
solution the cytoplasm swells separating from the cell wall in what we
know as plasmosis.
Active transport. It takes place in the movement of molecules against the
concentration gradient. So it requires energy in the form of the molecule ATP;
also it needs the help of the proteins incrusted in the membrane called carrier
proteins used to transport big molecules and vesicles. There are different
forms of active transport:

9. o Sodium Potassium pump mechanism: This mechanism is used in
neurons to excite them and create a difference in potential to create an
electrical current but also is used after they have been excited to go
back to normality. It consists in the change of the concentration of
ions; the mechanism expels 3 Na+ for every 2K+. Creating the
difference in potential.
o Exocytosis: Is a transport used by vesicles produced by the Golgi
apparatus. This type of transport is used to export substances. In it the
vesicle joins the membrane and breaks it expelling the substances.
Afterward the remaining vesicle covers the space opened.
o Endocytosis. In it the opposite thing occurs. The membrane deforms
doing invagination and forms a vesicle that traps substances and which
then lefts the membrane. Finally the space left is shelled.
o Phagocytosis. It can be done by microorganisms such as for example
bacteria. In it the cell forms pseudopods and traps the substance. This
is the case of phagocytes (white blood cells) which engulf particles
that need to be eliminated. Phagocytes are the only cells which can
leave the blood to eat microorganisms and defend our body. So this
system works with very big particles and some microorganisms (like
this is how we think chloroplasts and mitochondria were introduced
into eukaryotic cells.
We find that for carrying out nutrition, enzymes are very important as for
breaking substrates we need what is called the activation energy and with enzymes this
energy needed is much lower. So enzymes they are biocatalyzers that speed up chemical
reactions. For example we find that without enzymes we would need 2 days to break
down urea.
We find that all enzymes are proteins so they are made of amino acids and for
naming them we put the name of the substrate (the substances that react with the
enzyme) plus –ase.

10. Also we find that these enzymes are very specific as they can only work with
one type of substrate this is like this because of the key and the lock hypothesis which
establishes that enzymes are perfectly adapted to the substrate. So the substrate fits
exactly on the active site (the place which allows the enzyme to act as a catalyst). The
substrate reacts and forms the product that leaves the enzyme. So the only thing that
changes is the substrate not the enzyme.
Enzymes need specific conditions to work which are keep through homeostasis.
When we increase temperature the enzymes work better. However at one point the
enzyme’s activity start to decrease as when the temperature is very high the enzymes
vibrate and denature. Which means that they lose their native state (their 3 dimensional
structure) and cannot work any longer; however they keep the same amino acids and
sometimes they can be fixed. This is the reason why when we have hypothermia
enzymes do not work well; so we can say that the optimum temperature for enzymes is
37 degrees although each enzyme has a specific optimum temperature.
The same occurs with ph. Enzymes need an optimum ph that varies a lot
between enzymes. For example Pepsin works with a very acidic ph meanwhile amylase
works in alkaline ph. However the rule is that normally enzymes work badly with
extremes in ph.
Sometimes enzymes need inhibitors or activators to work which usually are ions
floating around the enzyme. Activators help the enzyme be in its native state and
activators change the structure of the enzyme so that the substrate doesn’t fit.
PROKARYOTIC CELLS.
The main difference between Prokaryotic and Eukaryotic cells is that Eukaryotic
cells have their DNA organized in a nucleus meanwhile Prokaryotic cells do not have a
nucleus. Prokaryotic cells have their DNA floating in the cytoplasm but also they have
rings of DNA which are never found in Eukaryotic cells.
Also Prokaryotic cells characterize for having a cell membrane, a cell wall
(although it is very different from the cell wall in plant cells) and a capsule that in the
case of bacteria makes some of them resistant to antibiotics.
Moreover ribosomes are different as they are smaller and thinner although the
function is the same (70s in comparison to eukaryotic cells where they are 80s). Finally
we find that Prokaryotic cells also have the Prokaryotic flagellum which is very typical
of bacterial and Pilli surrounding the capsule.
EUKARIOTIC CELLS: ANIMAL AND PLANT CELLS.
They are 2 types of cells. We find with animal and plant cells, both cells have a
nucleus, a cell membrane, cytoplasm and mitochondria. However we find that plant
cells in difference with animal cells have a cell wall which gives a polygonal shape to
the cell and which is made of cellulose which is a polysaccharide, chloroplast in where

11. photosynthesis takes place and where we can find chlorophyll and bigger vacuoles
than animal cell ones. Also we find that plant cells store starch for energy. Instead
animal cells have lysosomes and centrioles and store a substance called glycogen.
CELLULAR CYCLE.
INTHERPASE.
Is the period in which the cell is not dividing. This is an active phase because the
cell carries out metabolism. In this phase there are no chromosomes in the nucleus, but
only chromatin.
CELLULAR REPRODUCTION.
There are 2 types of cellular reproduction:
Mitosis: In this process you start with 1 diploid cell (2n) and you end with 2 diploid
cells. These daughters are identical to the mother cell. So we can say that organisms use
this process to grow and to renew old structures so it is carried anywhere in our body.
The nucleus divides in 4 phases:
1. Prophase. This is the longest phase. In it, the nuclear membrane disintegrates
and the nucleoli disappear. Also, strands of chromatin condense being
twisted forming chromosomes. Centrioles duplicate and the achromatic
spindle starts forming.

12. 2. Metaphase. In this phase chromosomes line up at the equator of the spindle.
3. Anaphase. In this phase chromosomes are broken into sister chromatids. One
chromatid is exactly the same as the other. Also, the fibers of the spindle
shorten pulling chromosomes apart.
46 chromosomes - 46 chromatids
- 46 chromatids.
Structure of a chromosome:
Each cell of a human being has 46 chromosomes and 23 pairs of
homologous chromosomes which are those chromosomes that have the
same type characteristics in the same places but no necessarily identical
genetic information.
4. Telophase. On this phase the nuclear membrane is organized again and the
nucleoli reappear. Also, the chromatids turn into chromatin again.

13. Cytokinesis.
When the Telophase ends and the nucleus is finally divided,
cytokinesis begins. During this process the cytoplasm divides and the
organelles are equally distributed. Animal cells are separated by a
process called pinchi up, instead plant cells are not separated but they just
build an internal wall which divides the 2 new cells. When the
cytokinesis ends the new cells begin interphase until they are able of
dividing again.
Meiosis. In the case of humans you start with 1 cell 2n with 46 chromosomes and at
the end you end up with 4 cells of 23 chromosomes each that are not identical to the
mother cell; so this process is called reduction meiosis as you halve the number of
chromosomes. Of these 23 chromosomes 22 are octosomesand 1 is a heterochromosome
which is involved in sexual reproduction. These chromosomes do not have their
homologous chromosome which is obtained from the other gamete in reproduction. All
the chromosomes are represented ordered in the Ideogram and disordered in the
Karyotype.
So we find that meiosis is used to produce gametes such as sperm cells or
ovules. However we find that meiosis is only realized in the gonads (testicles, ovaries,
pollen sacs and ovules). In men meiosis starts during puberty meanwhile with women it
occurs when she is an embryo.
The fact that the gametes are not identical to the mother cell is very important as
it enables evolution.
In this process you have 8 phases in 2 successive divisions:
Prophase I: It is the longer phase. In it the nuclear membrane and the nucleoli
disintegrate and the centrioles appear as during mitosis. The difference is that
here the chromosomes look for their homologous chromosome. The 2
homologous chromosomes stay very close together and exchange information.
So fragments of chromosomes are physically exchanged in what we know as

14. crossing over or synapse which is a cytological process; when this occurs the
exchange of genes occurs in what we know as recombination which is a
genetic process. So at the end we have a gamete with a chromosome with
different information from the beginning and with mixed information from the
father and the mother. In other words my cells have all the information from
my father and my mother; my gametes have a mixture of both.
After exchanging the genetic information the chromosomes form tetrads.
Metaphase I: in it the centrioles form the achromatic spindle and the tetrads
line up in the equator.
Anaphase I: Tetrads are separated. So 1 chromosome goes to one side and the
other to the other side.
Telophase I: This phase occurs very quickly. In it the cell divides in 2 each
one with 23 chromosomes instead of 46.
Prophase II: You start with 23 chromosomes and the same happens but this
time information is not exchanged. As the homologous chromosomes are
separated in different cells.

15. Metaphase II: The chromosomes are organized in the equator.
Anaphase II: Chromatids are separated as in mitosis so that you have 23
chromatids and 23 chromatids.
Telophase II: the cell divides in 2 so that at the end you have 4 cells with 23
chromatids. So you end with 4 haploid cells.
How you know haploid cells are called gametes. When the gamete of one
individual is going to join the game of another individual the chromatid create its sister
chromatid so the gamete has 23 chromosomes and the new cell (the embryo) contains
46 chromosomes and the homologous chromosomes are together again.
This process creates variation in Prophase I and in the combination of gametes
during fertilization. Another source of variation is mutation. The first to only happen in
sexual reproduction this is the reason why this process is so important.
PARTS OF THE CELLS:
1. Cell Membrane.
Structure, it is formed by a double layer of phospholipids and proteins. It
also has glucids that work as receptors and we find that it is partially
permeable because it lets some substances go through it.
Function, it has the function of protecting the cell, exchanging
substances and reaccepting different substances such as hormones.

16. 2. Golgi body.
Structure, it is formed by membranes piled onto each other surrounded by
vesicles.
Function, it´s function is to produce Lysosomes and vesicles to be exported
out of the cell and that carry different substances.
3. Ribosomes.
Structure, they are small particles formed by two subunits. They are
different in prokaryotic cells. They can be attached to the Rough
Endoplasmic Reticulum or isolated in the cytoplasm.
Function, their function is the synthesis of proteins. They read RNA and
they transform it into proteins. As we have different genes (fragment of
DNA that codes for a protein), we have different proteins.
4. Rough Endoplasmic Reticulum (RER)
Structure, It´s a set of interconnected membranes specialized in the
transport of proteins.
Function, The ribosomes creates the proteins and this set of membranes
transport the proteins.
5. Smooth endoplasmic reticulum (REL)
Structure, set of interconnect membranes specialized on the transport of
lipids.
Function, it transforms and transports lipids.

17. 6. Nucleus.
It controls the activity of the cells. It’s surrounded by a membrane and it
contains DNA.
Parts:
o Chromatin (DNA + protein)
When the cell is going to divide it condenses and forms
chromosomes. So we can say that chromatin and chromosomes
are only different in structure. All human cells have 46
chromosomes except sperms and ovules that have 23. They are
responsible of genetic information.
o Nucleolus
 Structure, 1 or 2 capsules inside de nucleus.
 Function, creation of ribosomes.
o Nuclear membrane
 Structure, double layer with the same structure of the cell
membrane and with lot of pores for allowing RNA to go
outside. This RNA goes to the ribosomes where they are
traduced into proteins.

Function, It protects the nucleus and allows the exchange
of substances. (RNAm)
o Nucleoplasm.
7. Centrioles.
Structure, they are only present in animal cells and they are formed by 2
cylinders made up of micro tubes.

18. Function, they are responsible of cellular division and as a base of cilia
and flagella in sperm cells for example.
8. Mitochondrion.
Structure, it is formed by a double membrane. The inner membrane is
folded forming cristae and inside this crestae there is a liquid called
MATRIX in which there is DNA floating. Because they have DNA
inside scientists believe that once they could have been living things in
what it is known as the Endosymbiosis Hypothesis. This fact is very
important for evolution because we inherit mitochondria from the
mother’s ovule so the DNA inside them is the DNA from our ancestors
with few variations through mutation.
Function, it carries out cellular respiration.
It takes: Glucose + O2 for, CO2 + H2O + ENERGY. (Transported
by the molecule ATP)
9. Lysosome.
Structure, it is a vesicle containing digestive enzymes and that is only
present in animal cells.
Function, their function is to destroy old parts of the cells. For this the
Lysosome opens and releases the digestive enzymes which destroy the
old parts eating them. They know what they have to eat thanks to
chemical signals. This is the reason why Lysosomes are mostly present
in old cells.
10. Cytoskeleton filaments.
Structure, it is formed by filaments of proteins that can be assembled if
the cells need them to do so.

19. Their function is to move organelles where the cells need them and to
keep the shape of the cell.
11. Cytoplasm.
Liquid in which all organelles are and in which chemical reactions take
place.
12. Cell wall.
Structure, it has an structure made of cellulose which is an
polysaccharide The cell wall is only present on plant cells.
Function, it gives a polygonal shape to the plant cell and protects it
against osmotic pressure. This means that it regulates the entrance of
water so the cell doesn’t explode for having too much water.
13. Vacuole.
Structure, it is a sac containing water and toxic dissolved and colored
substances. Animal cells also have vacuoles but they are much smaller.
Function, their main function is to store substances although they are
also important for the Hydro skeleton because they help to hold the plant.
14. Chloroplast
Structure, it has a structure formed by a double membrane, DNA and
small membranes inside. If these small membranes are pilled they are
called Grana thylakoids but if they are extended they are
calledstromathylakoids. These membranes contain chlorophyll and are
find floating on a liquid called Strama.

20. Function, they carry out photosynthesis thanks to that they have
chlorophyll a pigment substance that can be edited by light. That is the
reason why this organelle is only found on plant cells. You need an
electron microscope that functions with a ray of electrons instead of
light, for seeing the interior of organelles.