Presentación sobre las Células. Teoría de 4 de la ESO en ingles con links a videos

1. CELLS

2. BRAINSTORMING….
• What is the basic unit of all living things?
• What are the two broad categories of
cells?
• What do you remember about the basic
structure of a cell?
• List the cell organelles

3. CELLULAR THEORY
✔ Cells were discovered in 1677 by Robert
Hooke, from a layer of cork.
✔ In 1838, Mathias Schleiden (botanist) and
Theodor Schwann (zoologist) proposed
part of the Cellular Theory (*).
✔ Since then, this theory has gradually been
completed thanks to new scientific and
technological discoveries. The theory can
be summarized in the following way
1.All living beings are made up of cells.
2. Cells are the smallest unit of beings which
have a life of their own.
3. All cells come from another cell *
(proposed by Virchow).
4.Every single cell can work independently,
although in a coordinated way.

4. ✔Why was the microscope so
important for the
development of biology?
✔Are microorganisms visible to
the naked eye?
✔What is a microscope used
for?
✔What’s needed to look at a
sample under the
microscope?

5. 1.1. Cell structure
All cells exhibit a common basic structure:
⮚A cell membrane, a semipermeable membrane
that controls what enters and leaves the cell’s
interior
⮚The cytoplasm, the area where all the chemical
reactions related to the cell’s activity take place
(cell organelles)
⮚Genetic material: Organic biomolecules (DNA,
RNA) that directs all the cell functions = control
system

7. 1.2. Cell’s vital functions
Cells are the building blocks of life and perform the three vital functions
VITAL FUNCTIONS
NUTRITION
To transform nutrients into
energy for the cell’s activities
INTERACTION
To detect internal/external
changes and adapt to them
REPRODUCTION
1.Unicellular organisms= the
formation of new individuals.
2.Multicellular organisms=the
growth of the body structures

8. A. Nutrition
This key function allows cells to
obtain nutrients and transform them
into energy (cell respiration).
This energy will be used by cells to
renew their cellular structures, as
well as, for carrying the rest of cell’s
functions.
These transformations happen in the
cytoplasm through a process called
metabolism. This constitute the basis
of cell life
As a result of the cell metabolism,
waste products are produced and
they must to be expelled to the
external environment.
Types of nutrition:
1.Autotrophic nutrition
2.Heterotrophic nutrition
What is metabolism?
This term refers to the set of chemical
processes that happens in the cell’s
interior.

9. B. Interaction
This function allows cell to communicate
with the external environment.
Meaning, cells adapt to changes that
occur around them.
Cell would not be able to survive if this
function did not exist. They would be
unable to activate the essential
mechanisms needed to maintain their
vital activity

10. C. Reproduction
Reproduction refers to the
formation of new cells from
existing ones.
1.In unicellular organisms=
production of new individuals.
2.Multicellular organisms=
a)replacement of dead cells
b) the growth of the
individual

11. 2. Types of cells
Cells are extremely small structures that can only be observed using a microscope
Their size can be measured in micrometres, which is equivalent to a thousandth
part or a millimetre

12. Cell differentiation is the process by which
cells change in structure and become
capable of carrying out special functions, in
other words, cell become different cells so
they can do different jobs.
Cells then form specialized groups of cells,
which join forming tissues and then organs.
There are needed changes at three
different levels
1.Changes in shape and size
2.Changes in function
3.Changes at a cytoplasmic level ( cell
organelles)

13. 2.1. Cell organization:
From an evolutionary point of view all cells come from a common ancestor
There are two types of cells:
Type of cells
Prokaryotic
They are simpler and
more primitive
Eukaryotic
These cells evolved
from prokaryotic
cells
Anaerobic and photosynthetic bacteria
combined with prokaryotic cells
through endosimbiosis and turned into
mitochondria and chloroplasts
respectively

14. Lynn Margulis – Endosymbiotic theory:
- Lynn Margulis (1960’s)
- Ancestors of mitochondria and chloroplasts
were engulfed by eukaryotic cells.
- Evidences: Mitochondria and chloroplasts ….
1. Have double membranes.
2. Reproduce on their own
3. Have their own ribosomes

16. PROKARYOTE VS EUKARYOTE

17. 3. PROKARYOTIC CELLS

18. DOMAINS RELATED TO PROKARYOTIC CELLS

19. REVIEW: Taxonomic classification of living
things

20. 4. EUKARYOTIC CELLS
They are more complex and have a series of advantages over prokaryotic cells.
Their cytoplasm contains a wide
range of structures that are
specialized in performing different
functions = Cell organelles
Genetic material is found in the
nucleus. This way, it is protected and
provides better cell stability
Eukaryotic cells have a cytoskeleton, a
microscopic network of protein filaments and
microtubules. Its function is to maintain the
cell’s shape and internal organization. It also
plays a role in the cell movements

21. 4.1. ORGANELLES
What are the cell organelles?
They are membranous structures found in the cytoplasm. There are different organelles with
different jobs, so each organelle is made up of the biomolecules needed to perform its functions
1. Cell membrane
2. Cytoplasm
3. Ribosomes
4. Lysosomes
5. Endoplasmic reticulum ( RER/ SER)
6. Vacuoles
7. Golgi apparatus
8. Mitochondria
9. Chloroplasts
10. Cilia
11. Flagella
12. Nucleus

22. NON- MEMBRANOUS CELL ORGANELLES
RIBOSOMES: (They are the exception , as
they are not membranous structures)
They are spherical shaped organelles with
no membrane.
They can be found scattered throughout
the cytoplasm or attached to the rough
endoplasmic reticulum.
They are in charge of protein synthesis
MEMBRANOUS CELL ORGANELLES
CATEGORIES:
1. CELL ORGANELLES THAT PROCESS
NUTRIENTS
Lysosomes, vacuoles, endoplasmic
reticulum, Golgi apparatus
2. CELL ORGANELLES THAT PRODUCE
ENERGY
Mitochondria / chloroplasts
3. CELL ORGANELLES INVOLVE IN
MOVEMENT
Cilia , flagella, centrioles

23. 4.1.1. Organelles that process nutrients

24. 4.1.1. Organelles that process nutrients
LYSOSOMES They are small vesicles that contain subtances capable of digesting molecules
captured by cell. They contain digestive enzymes
ENDOPLASMIC
RETICULUM
It’s a very complex set of tubules and vesicles responsible for manufacturing and
transporting different substances, such as lipids and proteins. There are two
types:
-Rough endoplasmic reticulum: to synthetyse proteins
-Smooth endoplasmic reticulum: to produce lipids
VACUOLES Structures in charge of storing different substances (mainly water). In animal
cells they are more numerous but smaller. In plant cells there is a central and big
vacuole.
GOLGI APPARATUS This cell organelle is formed by grouped vesicles and flattened sacs; it take
substances from the endoplasmic reticulum, modifies them and introduces them
into the vesicles for secretion

25. 4.1.1. Organelles that produces energy
Mitochondria Chloroplasts
They are cylindrical organelles
made up of a double
membrane.
The external membrane is
smooth and the internal one
has folds (cristae). Inside is the
matrix, which is mainly made
up of genetic material,
ribosomes and enzymes
Mitochondria are considered
the power plants of the
eukaryotic cells, as they are in
charge of obtaining energy (
cell respiration).
They are egg-shaped organelles
with a double membrane.
They have a series of disc-
shaped sacs name thylakoids,
which contain the pigment that
gives them their green colour.
Chloroplasts synthesize organic
molecules from inorganic ones
using chemical energy obtained
from the Sun = photosynthesis.
These organelles are only found
in the cells of photosynthetic
organisms ( plants and algae)

27. 4.2. Organelles involved in cell mobility
Cilia and flagella
They are mobile cell organelles.
They are formed by protein fibres from
the cytoskeleton
Their movement is coordinated by a
structure known as centriole.
The centriole is formed by protein
tubules arranged like cilia and flagella.
This is also involved in cellular division
Certain eukaryotic cells are able to move in two
different ways:
1.Using their appendixes ( cilia and flagella)
2.By changing the viscosity of their cytoplasm

28. 4.2.2.Changes in the viscosity of the cytoplasm
Proteins found in the cytoskeleton
are responsible for changes in the
viscosity of cytoplasm.
They do this by grouping together
or separating themselves. They
produce pseudopodia, an
extension of cytoplasm, and
modify the shape of the cell.
Pseudopodia are also used to
surround and capture certain
materials from the environment (
microbes, food particles…). This
process is known as phagocytosis

29. 4.3. Nucleus
Nucleus
It is the control centre of the cell. This organelle contains the genetic material.
It is normally located in the centre of the cell. In some cases, such as secreting cells and many plant cells, it can
be found in peripheral areas.
Its structures varies depending on the moment in life of the cell. It has two different structures:
1.INTERPHASE NUCLEUS (when the cell is not dividing)
2.NUCLEAR DIVISION (when the cell is diving)

30. Interphase nucleus Nuclear division
It has a porous double membrane that surrounds the
nucleoplasm, which is similar to cytoplasm.
Inside the nucleoplasm there is chromatin, a
substance formed by the double helix of DNA joined
to histones (proteins) and nucleolus, a spherical
organelle involved in the synthesis of ribosomes
Once cell division begins, the nucleus changes deeply:
Chromatin condenses into chromosomes.
Chromosomes are X-shaped structures.
Each chromosome is made up of two chromatin
filaments called chromatids, which are joined by a
centromere. Both chromatids are identical, so the
genetic information is duplicated. The centromere
separates two regions in each chromatid, names arms

31. The number of chromosomes in gametes ( sex cells) varies from somatic cells.
1.The haploid number (n) is the number or chromosomes in a gamete.
2.The diploid number (2n) refers to the number or chromosomes in somatic cells.
There are two sets of haploid cells in a somatic cell, one from each parent

32. Animal cell vs plant cell
Tour inside the cell

33. The cell cycle is the series of events
that take place in a cell that cause the
division of a parent cell into two
daughter cells.
These events include the duplication
of its DNA (DNA replication) and some
of its organelles, and subsequently
the partitioning of its cytoplasm and
other components into two daughter
cells in a process called cell division.
Phases:
a)Interphase
- G1: growth
-S: duplication of DNA
-G2: cell functions/ preparation for
mitosis
a)Mitosis (M)
The cell cycle

34. https://www.youtube.com/watch?v=DwAFZb8juMQ

35. Mitosis. Prophase
1. Chromatin fibres thicken and
shorten to form
chromosomes.
2. The nucleolus disappears
3. Protein fibres appear between
both poles of the cell to form the
mitotic spindle
1. The nuclear membrane
disappears, so chromosomes
can move freely around the
cytoplasm.

36. Mitosis.
Metaphase
1. Chromosome bond to the
mitotic spindle fibres using their
centromeres.
2. This union takes place in the
equator of the cell.
3. Sister chromatids belonging to
each chromosome point to the
opposite poles of the cell

37. Mitosis. Anaphase
1. The mitotic spindle fibres break
into equal halves. This causes
the chromosome’s centromere
to break. As a result, the two
chromatids that made up each
chromosome separate into two
unconnected half fibres.
2. The mitotic spindle fibres
contract, pulling the chromatids
towards the opposite poles.
3. From this point onwards,
chromatids are considered to
be independent chromosomes

38. Mitosis. Telophase
1. Once chromatids move to
the ends of the poles, the
remains of the mitotic
spindle fibres disappear.
2. A new nuclear membrane
surrounds each group of
chromatids, forming two
new nuclei.
3. Chromatids expand and
turn into chromatin
4. The nucleolus reappears

39. Once mitosis ends, the division of the cytoplasm takes place and cell organelles are shared.
This process is referred to as cytokinesis and it can take place in two ways:
1.In animal cells, the cytoplasm stretches, thins out and eventually separates.
1.In plant cells, a wall forms which divides the cytoplasm in half
Cytokinesis

43. Basics about meiosis:
• Meiosis is the process in eukaryotic, sexually-reproducing animals that reduces the number of
chromosomes in a cell before reproduction
• Function of meiosis:
• Meiosis is necessary for many sexually-reproducing animals to ensure the same number of
chromosomes in the offspring as in the parents. The act of fertilization includes two cells fusing
together to become a new zygote.
• Meiosis consists of two divisions, both of which follow the same stages as mitosis (prophase,
metaphase, anaphase, telophase).
• Meiosis is preceded by interphase, in which DNA is replicated to produce chromosomes consisting of
two sister chromatids.
• A second growth phase called interkinesis may occur between meiosis I and II, however no DNA
replication occurs in this stage.

46. What is crossing over?
The exchange of chromosomal segments
between two non-sister chromatids
Why does crossing over occur?
To provide genetic variation during meiosis as
crossing over ensures a combination of the
maternal and paternal genes we inherited

47. Meiosis. Prophase I
✔ Chromosomes condense
✔ Nuclear membrane
dissolves
✔ Homologous chromosomes
form bivalents
✔ Crossing over occurs

48. Meiosis. Metaphase I
Spindle fibres from opposing
centrosomes connect to
bivalents (at centromeres)
and align them along the
middle of the cell

49. Meiosis. Anaphase I
✔Spindle fibres contract
and split the bivalent.
✔Homologous
chromosomes move to
opposite poles of the cell

50. Meiosis. Telophase I
✔ Chromosomes decondense
✔ Nuclear membrane may reform
✔ Cell divides (cytokinesis) to form
two haploid daughter cells

51. Meiosis II. Prophase II
✔ Chromosomes condense
✔ Nuclear membrane
dissolves
✔ Centrosomes move to
opposite poles
(perpendicular to before)
The second division separates sister chromatids (these chromatids may
not be identical due to crossing over in prophase I)

52. Meiosis. Metaphase II
✔ Spindle fibres from
opposing centrosomes
attach to chromosomes
(at centromere) and
align them along the
cell equator

53. Meiosis. Anaphase II
✔ Spindle fibres contract
and separate the sister
chromatids.
✔ Chromatids (now called
chromosomes) move to
opposite poles

54. Meiosis. Telophase II
✔ Chromosomes decondense
✔ Nuclear membrane
reforms
✔ Cells divide (cytokinesis) to
form four haploid daughter
cells
The final outcome of meiosis is the production of
four haploid daughter cells.
These cells may all be genetically distinct if crossing
over occurs in prophase I (causes recombination of
sister chromatids)