Cell Structure and Organisation
Key Question: What is life made of?
Life generally consists of : ability to move, ability to reproduce and ability to take in use nutrients for its growth
Learning Outcomes
• Identify the main organelles and membranes in the cell (nucleus, mitochondria, cell surface membrane, cytoplasm, Golgi Apparatus, endoplasmic reticulum, cell wall, chloroplast, vacuole)
• Explain the various functions of different organelles
Learning Outcomes
• Compare the structure of plant and animal cells
• Describe the relationship between structure and function as seen in xylem vessels, root hair cells and red blood cells
• Differentiate between the levels of organisation in an organism
The term “cell” was first introduced by Robert Hooke in 1667 who examined thin slices of cork under a microscope
Cork cells (dead plant cells) as seen by Robert Hooke
What is a cell?
Cell is the basic unit of structure and function in an organism
It is the basic block of life
All organisms are composed of one (unicellular) or more cell (multicellular)
What is a cell?
A cell is like a factory. What do you think are the parts or functions of a factory that may be similar to the cell?
How do we study the parts of a cell?
• Use of microscopes-> light microscope (magnifies objects up to 1000x)-> electron microscope (magnifies objects to >200,000x)
Structure of the cellProtoplasm: •Each living cell consists of living material called protoplasm which is contained within the cell membrane.
•The protoplasm is made up of 70% water and 30% of other substances, most of which are proteins, carbohydrates and fats.
•The composition of protoplasm varies greatly from cell to cell.
Both Cells
Cell surface Membrane (plasma membrane)
Thin partially permeable membrane that surrounds the cytoplasm
Controls substances entering or leaving cell
Keeps cell content in placePPM is like a door that allows only some substances to cross it.
Cytoplasm: Is the part of the protoplasm between the cell surface membrane and the nucleus
Contains enzymes and a suspension of specialised structures called organelles
Site within cell in which most cell activities occur
Both Cells
(cytoplasm)
Organelles carry out various functions in the cell.
Nucleus:Small spherical structure consisting of nucleoplasm surrounded by a nuclear envelopeContains one or more nucleoli and chromatin
Both Cells
Nucleoplasm
Functions of the nucleus:
Controls cell activities such as growth and repair of worn-out parts
Involved in cell division
Functions of the nucleolusNucleolus: needed to
make ribosomes
Both Cells
Chromatin:
Network of long thread-like structures that control cell division
Each chromatin thread is made up of proteins and deoxyribonucleic acid (DNA)
Chromatin threads condense to become chromosomes (highly coiled structures) during cell division
Both Cells
Organelles- Endoplasmic reticulum (ER)• There are 2 types of ER – rough ER and smooth
ER.
Both Cells
Rough Endoplasmic reticulum (RER)• Outer surface appears rough and is
continuous with nuclear envelope
• Ribosomes attached to outer surface
• RER transports proteins made by ribosomes to Golgi apparatus for secretion out of cell
Both Cells
Smooth Endoplasmic reticulum (SER)• More tubular and may or may not be connected to RER
synthesises substances such as lipids and steroids (sex hormones)converts harmful substances into harmless materials (detoxification)
Both Cells
Golgi apparatus (Golgi body)
• Shaped like a disc• Consists of stack of flattened
spaces surrounded by membrane
• Vesicles can be seen fusing with one side of Golgi apparatus and pinching off on opposite side
• Golgi apparatus-> stores and modifies
substances made by ER (both SER and RER)
-> packages these substances in vesicles for secretion out of cell
Both Cells
Vesicles or vacuoles
• a vesicle is a relatively small intracellular, membrane-enclosed sac that stores or transports substances.
• Vacuoles store food and other materials needed by a cell.
Mitochondrion
Sausage-shaped like organelles; double membrane with inner membrane thrown into deep folds called cristae
Both Cells
inner compartment
outer membrane
matrix
cristae
Mitochondrion…• Site of aerobic respiration to release energy Site of aerobic respiration to release energy
from food used by cell for growth and from food used by cell for growth and reproductionreproduction
• During aerobic respiration, food substances are broken down to their molecules to release energy.
• This energy may be used by the cell to perform cell activities such as growth and reproduction.
Vacuoles
• Fluid filled spaced enclosed by membrane
• Store substances with cell
• Animal cell: many small vacuoles that contain water, food substances and enzymes- (digestive enzymes to digest invading bacteria); usually exist temporarily
vacuoles
Vacuoles
• Plant cell: large central vacuole containing cell sap (nutrients- sugars, amino acids, mineral salts, wastes, poisonous substances that deter animals from feeding on plant parts) enclosed by a tonoplast (partially permeable)
Cell Wall:
Rigid wall made of celluloseCell wall is fully permeable
Protects the cell from injury and gives plant cell a fixed shape
Plant Cell
lysosome
plasma membrane
cell wall
nucleolus
nucleus
mitochondrion
sap vacuole
chloroplast
cell wall of adjacent cell
Chloroplasts:
Oval structures
Contain a green pigment called chlorophyll
Carry out photosynthesis
Plant Cell
Differences between plant and animal cells
Feature Plant Cell Animal Cell
Cell Wall Present Absent
Vacuoles A single, large central vacuole
Vacuoles are small and many (temporary)
Chloroplasts Present in photosynthetic cells
Absent
Centrioles Absent Present
Specialized Cells, Tissues, Organs and Systems
There are many different groups of cells which have different structure, shapes and sizes
They are adapted to perform specific roles
Differentiation:- A process by which a cell becomes specialised for a specific function
Examples: Root hair cells Red blood cells Xylem vessels
Red Blood Cell – oxygen transport
No nucleus:- can carry more haemoglobin and thus more oxygen
Circular biconcave shape:
- Increase surface area to volume ratio of cell for diffusion of oxygen into and out at a faster rate
Contains haemoglobin:
-Combines with oxygen to form oxy-haemoglobin which transport oxygen from lungs to all parts of body
Root Hair Cell - absorption
Long and narrow protrusion of epidermal cell (root hair):
- increases surface area to volume ratio of cell so that water and mineral salts can be efficiently absorbed from the soil
The Xylem Vessel
xylem epidermis
phloem
cambium
xylem
thickened band
lumen
hollow vessel
long vessel
Transverse section through a dicotyledon stem to show the xylem
vessels
Xylem vessel
Dead Plant cells laid end to end (without nucleus and cytoplasm) with thickening cell walls Xylem vessels
Absence of cross walls or protoplasm
- enables water to move easily through the lumen
Long, hollow tubes formed from xylem cells laid end to end
- Allows water and
mineral salts to be
conducted from roots to
stem and leaves
Lignin deposited on walls of xylem vessels
- strengthens wall and prevents vessels from collapsing
Xylem Vessels – conduction and support
xylem vessels bundled together
- provides mechanical support to plant
Cell is the basic unit of structure and function in an organism
It is the basic block of life
From cells to tissues to organs to systems!
TissuesDefined as a group of similar cells working together to perform a specific function
There are simple tissues and complex tissues
Example of tissues:- Epithelial tissues- Connective tissue- Muscles tissue- Nervous tissue
Simple tissues (cells of the same type)
Animal tissues Plant tissuesEpithelial tissues
Epithelial tissues
These are sheets of cells which
cover the external surface or line the
cavities of the body
Muscle tissuesMuscle tissues
These are concerned with
body movements by contracting
epithelium lining blood
vessels
epithelium covering the
ovary
epithelium lining the trachea
muscles in the walls of the
intestine
muscles of the heart
Epidermis
Covering tissues of leaves and stems
Animal tissues Plant tissues
Complex tissues (several types of cells)
Connective tissuesConnective tissues
These join together body structures, providing protection and support
Nervous tissuesNervous tissues
These are concerned with the conduction of nerve impulses throughout the body
bloodnerve tissue of the brain
Vascular tissues-xylem and phloem tissue
OrgansA structure made of different types of tissues working together to perform specific functions
There is division of labour among the organs
Organs in animals
Stomach (store food, digest and churn)• glandular tissues secrete digestive juices• Muscular tissues causes stomach to contract
and mix food with digestive juices• Nervous tissue coordinates actions of stomach
Plant organsPlant organs
Leaves- Make food
Stem-transports water with dissolved mineral salts from roots to leaves and food from leaves to other plant parts- gives support to plant above ground
SystemsSeveral organs working together for a common purpose make up an organ system
Examples:- Digestive system
- Respiratory system- Nervous system- Circulatory system
small intestinelarge intestine
liver stomach
pancreasgall bladder
tonguesalivaryglands
oesophagus
rectum
Digestive system
Division of labour in cells
• In each cell, there are organelles specially designed to perform a specific job.
• For example: chloroplasts allow plant to make food, mitochondria enables respiration to take place...
• Division of labour (breakdown of workload to smaller and more specific tasks) helps individual cells function more efficiently
SummaryFeatures Plant Cells Animal Cells
Nucleus √ √
Cell membrane √ √
Cytoplasm √ √
Mitochondria √ √
Endoplasmic Reticulum
√ √
Golgi Apparatus √ √
Cell Wall √ X
Chloroplasts √ X
Vacuole 1 large vacuole Numerous small vacuoles
Tonoplast √ X
Summary
Specialized Cells
Root hairs Red Blood Cells Xylem Vessels
Absorption of water & mineral salts
Transport oxygen Transport of water & mineral salts
Example
Function Function Function
* How are they adapted for their functions?