3.1. tissues cells and organelles

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Edexcel AS Biology (8BIO 1) Mo Idriss, Quick Revision Notes

1 Unit 2: Developments, Plants and the Environment Topic 3: The voice of the Genome

Cells and Organelles

Learning

O

bjective(s)

After studying this section, you will be able to:

Distinguish between eukaryotic and prokaryotic cells in terms of their structureand ultrastructure

Describe the ultrastructure of an animal (eukaryotic) cell (nucleus, nucleolus,ribosomes, rough and smooth endoplasmic reticulum, mitochondria, centrioles,

lysosomes, and Golgi apparatus) and recognise these organelles from EM images

Explain the role of the rough endoplasmic reticulum (rER) and the Golgiapparatus in protein transport within cells and including its role in formation of

extracellular enzymes

Prokaryotes and Eukaryotes

Living things are made of cells which contain organelles such as the cell membrane and

ribosomes sub-cellular structures that carry out specific functions. Some living things are

made of only one cell (unicellular e.g. cholera bacterium and amoeba) whilst many others are

made of many cells (multicellular e.g. humans and most plants).

All living organisms can be divided into two types: Prokaryotic and Eukaryotic organisms.

Prokaryotic organisms are simple, one celled organisms with a primitive (pro) nucleus (karyote)

which is not surrounded by a membrane. Their cells are also smaller; they lack membrane-

bound organelles like mitochondria and ER, have circular DNA, and have smaller ribosomes.

Prokaryotic cells are bacteria.

Eukaryotic organisms are made of one or more eukaryotic cells. Eukaryotic cells are larger and

more complex than prokaryotic ones, have a true nucleus (Eukaryote) surrounded by a nuclear

envelope and containing linear DNA, as well as other membrane bound organelles like

mitochondria, ER (endoplasmic reticulum) and Golgi apparatus.

The ultrastructure refers to the structure of the cell as seen under a powerful microscope like

an EM. The diagram on the next page shows the ultrastructure of an animal cell. We need to

know the structure in relation to the function of the following organelles:

1-nucleus, 2-nucleolus, 3-ribosomes, 4-rough and smooth endoplasmic reticulum,

5-mitochondria, 6 centrioles, 7-lysosomes, and 8-Golgi apparatus.

1. PowerPoint presentation on ultrastructure of animal cells; 2. Look at the diagram overleaf and/or

poster; 3. Annotate diagram provided.


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Mitochondrion

Surrounded by double

membrane. Inner membrane

folded into cristae around a

central matrix. Matrix contains

DNA & ribosomes. Site of aerobic

respiration,therefore

abundant in

active cells.

Golgi Apparatus

Cytoplasm

Smooth ER

------------ ER

Nucleus

Nucleolus

----------------------

Lysosome Plasma Membrane

------------------------

Two hollow cylinders

arranged at right angles

to each other.

Involved in spindle

formation during cell

division

Ultrastructure of animal cell. Complete the annotation make some notes about structure and function

of each organelle you may draw a diagram to help your explanation


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Make sure you can recognise the different organelles from the electron microscope images for (A)

Nucleus. Nucleoli are observed inside the nucleus. (B) Rough endoplasmic reticulum. Numerous

ribosomes (dark spots) bind to the surface. (C) Golgi body. The top is the cis side and the bottom is the

trans side. (D) Lysosome. Material being degraded is observed on the inside of this organelle. (E)

Peroxisome. A crystalline, dark region is observed at the centre. (F) Mitochondria. The dark granules

contain calcium. (G) Chloroplast. Grana are the membrane structures observed in the dark

Protein Modification and transport in Eukaryotes

The two organelles involved in this are the Endoplasmic Reticulum (ER) and the Golgi body.

ER is classified into rough ER and smooth ER depending on its structure. The rough ER with

attached ribosomes are where protein synthesis occurs. Newly synthesised proteins are also

stored here. Some initial processing of proteins may also occur here for example addition of


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carbohydrates. Eventually the proteins are pinched off in vesicles from the end of the Rough ER

and moved to the Golgi for modification into other products that the cell needs.

The Golgi body (also called Golgi complex or Golgi apparatus) is an organelle shaped like stacks

of several layers of flat smooth ER (Fig. 11-8C). The function of the Golgi apparatus is to further

process proteins received from the Rough ER into products depending on the needs of the cell,

and then send them on to their destinations.

The cis side of the Golgi is the face that receives proteins from Rough ER and the trans side is

where they are shipped off from.

Some of the modifications of proteins within the Golgi include formation of lysosomes, which

contain digestive enzymes that are used to recycle cell organelles inside cells or for

export/secretion out of the cells.

Modifications may also be by addition of polysaccharides, phosphate groups or sulphate groups

to the proteins.

The smooth ER is involved in various functions such as the synthesis of steroids, lipids &

phospholipids, glycogen metabolism, calcium ion regulation, and intracellular digestion.


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Differences between Plant and Animal cells

We have already outlined the differences between prokaryotes and eukaryotes. Plant and

animal cells as well as fungal cells are eukaryotic cells. The organelles we have described in the

section above are for animal cells. Plant cells are eukaryotic and share most of the

features/organelles described; however there are some differences between plant and animalcells which we will now discuss in the form of the table below.

1. Label the plant cell on the right.2. How does it differ from the animal

cell described on page 3 above?

3. In the form of a table (below),describe the structure and function

of the following plant organelles: cell

wall, chloroplasts, amyloplasts,

vacuole, tonoplast, plasmodesmata,

pits and middle lamella

A generalised plant cell

Organelle Structure Function

Cell Wall Rigid layer of cellulose and other

polysaccharides, proteins and

sometime lignin on the outside of

the plasma membrane of a plant

cell. Divided into 1ry - deposited

while a cell is growing; typically

extensible & 2ry - innermost layer,

deposited after cell enlargement

has ceased, often lignified.

Chloroplast Small flat/disc shaped &surrounded by double membrane

and filled with gel called the

stroma. Inside are thylakoid

membranes which are stacked in

places to form grana. Grana are

linked together by lamellae.

Site of photosynthesis. Separateenzymes are located on grana and in

stroma


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Organelle Structure Function

Plasmodesmata Small, cylindrical channels in the

cell walls of plants. They form

when parts of the endoplasmic

reticulum of a parent cell (during

cell division) get caught in the cellwall of the resulting daughter cells.

Act as bridges connecting the

cytoplasm of cells; important

for communication among cells. Allow

free movement of the contents and

can contract or dilate to allowdifferent sized molecules through.

Amyloplast Stores large amounts of starch, but no

chlorophyll, specialized for storage.

Abounds in storage tissues e.g. potato

Tonoplast

Vacuole

Single membrane which envelops

the central vacuole in plant cells.

It is relatively impermeable to

solutes but highly permeable to

water.

Large water filled and surrounded

by a single membrane (tonoplast).

For storage of metabolic wastes. May

also contain pigments that are water

soluble & phenolic compounds that

function in plant defense.

Pit

A region where the

secondary cell wall is

absent, but the primary

cell wall is present.

Middle Lamella


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This diagram represents a

prokaryotic (bacterial cell).

How does this cell differ fromeukaryotic (plant and animal) cells?

Feature

Prokaryotic Cell Eukaryotic Cell

Animal Cell Plant Cell

Nucleus with envelope

Membrane bound organelles

DNA found as

Flagella

Cell wall

Relative cell size

How Prokaryotic cells differ from Eukaryotic cells

Differences between prokaryotic and eukaryotic cells (Please complete)

Feature Prokaryotic (bacteria) Eukaryotic (plant/animal/fungi)

Size Small cells - 5m Large cells - 50mCapsule (protection) Present Absent

Cell wall Present (peptidoglycan) In fungi (chitin)In plants (cellulose)NOT in animals

Plasma membrane Present Present

Membrane bound organelles(indicate with examples

whether present or absent)

_________________________

_________________________

_________________________

_________________________

_________________________

_________________________

Nucleus- Nuclear envelope

- Nucleoli- Nature of DNA

Absent\ Absent

\ Absent_________________________

Present\ Present

\ Present____________________________

Centriole (for mitosis) Absent Only in animal cells


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Cellular Organisation

Multicellular organisms have many cells but

these cells are not randomly arranged. They are

specialised to carry out specific functions and

grouped into tissues. Structurally, cells ofmulticellular organisms are organized into four

levels:

Cells Tissues

Organs Organ systems

A tissue is a group of similar cells, that develop

from the same kind of cells and which work

together to perform a commonfunction; such as muscle tissue.

Some examples of animal tissues are

seen in the diagram on the right. They

include:

1. Connective tissue supportingtissue like bone and cartilage.

2. Epithelial tissue lines surfacesboth inside and outside thebody e.g. the skin is made

mainly of stratified epithelium.

3. Muscle tissue contracts to aid movement4. Nervous tissue in brain, spinal cord and nerves. Transmits electrical messages around

the body

Some examples of plant tissues are collenchyma and schlerenchyma tissues which are for

support as well as vascular/conductive tissue (xylem & phloem) which are for transporting

water and dissolved minerals/food.

Tissues are organised into organs the heart in humans; the root and leaf in plants are

examples of organs. Organs are groups of tissue collected into a structure to work together

effectively.


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The diagram shows a section through the plant organ, the Leaf.

Label it to show the different tissues it has.

In animals, many organs are then grouped together into systems to carry out a large scale

function. A good example of an organ system is the digestive system which consists of many

organs (stomach, liver, oesophagus, small intestine, pancreas e.t.c) which in turn consist of

many combinations of tissues.

3.1. tissues cells and organelles

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