Lesson 2: Cell structure & function
Living cell processes:
1. Nutrition – obtain food molecules
2. Digestion - which food particles are broken down into smaller soluble units suitable for cell use
with the help of enzymes.
3. Absorption - absorb water, minerals and other materials essential to life from their
environment.
4. Biosynthesis - all cells organize complex chemicals from simple building units or substances.
5. Excretion - by-products of all cell activities which are not needed for further cell functioning are
eliminated.
6. Egestion - insoluble, non-digested particles are eliminated by the cell.
7. Secretion - substances that are synthesized by the cells are expelled from the membrane. This
elimination process helps in the functioning of the body.
8. Movement – locomotion of cell by means a special structures like cilia or flagella
9. Irritability - cells respond or react to external factors or conditions around them.
10. Respiration - breaking down food molecules into chemical energy needed by all cells in order to
function
11. Reproduction - a cell copies or replicates its DNA and increases its number by cell division. It
gives rise to new cells as a result, organisms grow.
Principal part cell:
Cell membrane
Cytoplasm
Nucleus
Nucleus
o Covered with a membrane that allows materials to pass in and out.
o Often called the control center because it contains DNA
Nucleolus is where the ribosomes are formed and this structure can be found
both in plants and animals.
Cell membrane
o Semi-permeable membrane: facilitate the movementof molecule inside and
outside the plant or animal cell
allows only chosen substances to enter or leave cell which can protect
the cell from harmful substances.
o Often pictured as fluid mosaic model - its molecules are constantly moving.
: Phospholipid molecules move sideways within the membrane. Since the plasma
membrane is fluid, it can seal itself if it is damaged or broken.
Cytoplasm
o viscous fluid or jelly like where organelles are embedded
(under a surface)
o secures the organelles in plants and animals so that
they remain in place.
Mitochondria
o powerhouses of cells
o They produce much of the energy a plant or animal cell needs to carry out its functions.
o They are the centers of cellular respiration, a process in which energy-rich ATP (Adenosine
Triphosphate) that functions in energy storage and transfer is produced.
What is organelles?
a subcellular structure that has one or more specific jobs to perform in the cell, much like an organ
does in the body.
Vacuole
o storage area of the cell; water, food, and waste.
Animals vacuole: small
Plants vacuole: big (photosynthesis)
Endoplasmic reticulum
o series of tunnels throughout the cytoplasm
o transport proteins from one part of the
cell to another
o form a network of tiny canals through the cell
(both ER) formed by two parallel membranes
Two types of endoplasmic reticulum:
Smooth- ribosome free and functions in detoxification of lipids.
Rough - contains ribosomes and releases newly made protein from the cell.
Ribosome
o Protein factories of the cell
Golgi bodies
o Receive proteins and other compounds from the ER
o Package these materials and distribute them to the plant and animal parts of the cell.
Lysosomes
o Contain hydrolytic enzymes that can break things down.
o Pick up bacteria, food, and old organelles in plant and animal cell and break them into small
pieces that can be reused.
Cytoskeleton
o series of fibers made from proteins; gives it its shape.
Components of cytoskeleton:
Microtubules - absent in plant cell, it provide pathways for certain cellular molecules to move
about just as tracks are provided for railroad cars or trains.
- found in structures like the cilia and flagella which both aid in movement.
Intermediate filaments -they are found in durable structures such as hair, scales and fingernails.
They also help provide structure to the nuclear envelope. (absent in plant cell)
Microfilaments - pipe-like structures and help provide shape and movement for the cells.
Cell wall : plants
o rigid organelle composed of cellulose that gives plant cell its box-like shape.
Primary cell wall =outer layer. It expands as the cell grows
As the plant reaches its full size, a secondary wall develops inside the primary wall = to
strengthen
o Middle lamella which is composed of a jelly- like polysaccharide called pectin
o Both the primary and secondary walls are composed mainly of polysaccharide cellulose which is
commercially important as the main component of paper and cotton.
o Aside for cellulose, the secondary walls usually contain lignin, a complex organic compound that
adds hardness and rigidity to cell walls.
o Plastids are double membrane bound organelles found in plants; storage of pigments
o Types of Plastids include the Leucoplasts which are colorless organelles that store starch and
Chromoplasts which contain colored pigments like chloroplast.
Centrioles
o paired organelles found only in animal cell
o located near nucleus at right angle
o they are essential in building cilia and flagella and also as spindle fiber during cell division.
Differences:
Animal cells have centrioles, centrosomes (discussed under the cytoskeleton), and lysosomes,
whereas plant cells do not. Plant cells have a cell wall, chloroplasts, plasmodesmata, and
plastids used for storage, and a large central vacuole, whereas animal cells do not.
