Download NOTES 2.1 CELL STRUCTURE

IGCSE
BIOLOGY
Cellular organization
State that living organisms are made of cells
All animals, plants, fungi, protists, & bacteria are made of one or more cells.
Cells are the smallest unit of life.
Most human cells, like most other animal cells, have the following parts:
 nucleus
 cytoplasm
 cell membrane
 mitochondria
 ribosomes
Plant cells also have:
 cell wall
 chloroplasts
 permanent vacuole
1
Identify and describe the structure of a plant cell (palisade cell) and an animal cell (liver cell), as
seen under a light microscope.
palisade cell
liver cell
Photos produced by microscopes are called micrographs.
2
Light micrographs
Transverse section of upper part of leaf of a
Helleborus sp. showing epidermis and palisade
cells.
Light micrograph of a transverse section through a holly leaf, Ilex sp. .
Below the epidermis (top layer of cells), are two layers of column-like cells
known as palisade cells. These contain large numbers of chloroplasts and
are the principal sites of photosynthesis. Magnification: x240 at 35mm size.
Tea leaf. Light micrograph of a cross-section
through a tea (Camellia sinensis) leaf. The
upper and lower epidermis on the surfaces
of the leaf are blue. Under the upper
epidermis are palisade cells (brown), which
contain chloroplasts, the site of
photosynthesis. Beneath this a spongy
mesophyll layer with large spaces between
the cells. At bottom left, a stoma (pore) is
seen. Stomata allow gases and water to
enter and leave the plant. Magnification:
x230 when printed 10 centimeters wide.
3
Color enhanced freezefracture Scanning Electron
Micrograph (SEM) of leaf of
Lupin plant (Lupinus), showing
vascular bundle, epidermis,
palisade cells and spongy
mesophyll. Magnification
x540
Scanning Electron
Micrographs
Scanning electron micrograph of cross
fracture of the leaf Zinnia elegans, showing
the upper epidermis and palisade cells
within which are stored the chloroplast
(photosynthesis). X 2100.
Leaf section. Colored scanning
electron micrograph (SEM) of a
section through a fractured leaf.
At right is a single layer of cells
that forms the epidermis of the
leaf.
The top layer (seen here at left)
of the leaf interior is made up of
palisade mesophyll tissue.
One of the tightly packed
palisade cells (light green) has
been fractured open to reveal its
chloroplasts (orange/green), the
sites of photosynthesis.
4
Describe the differences in structure between typical animal and plant cells.
Generalized animal and plant cell
*Make sure you can label diagrams of animal and plant cells.
5
Describe the differences in structure between typical animal and plant cells.
PLANT CELLS
Have a rigid cell wall that helps them keep
their shape.
Plants manufacture their own food and use
chloroplasts to do that.
Usually have a large central vacuole.
ANIMAL CELLS
Do not have a cell wall and therefore require either
external or internal support from some kind of skeleton.
Have a shape related to their function.
Animals must eat their food because they cannot
photosynthesize.
Animal cells may have several small vacuoles, or none at all.
6
Relate the structures seen under the light microscope in the plant cell and in the animal cell to
their functions.
Animal cells and plant cells have some organelles in common.
organelle
function
nucleus
contains genetic material, which controls the activities of the cell
cytoplasm
most chemical processes take place here, controlled by enzymes
cell membrane controls the movement of substances into and out of the cell
mitochondria
most energy is released by respiration here
ribosomes
protein synthesis happens here
Plant cells also have a cell wall, and often have chloroplasts and a permanent vacuole.
organelle
function
cell wall
strengthens the cell
chloroplasts
contain chlorophyll, which absorbs light energy for
photosynthesis
permanent
vacuole
filled with cell sap to help keep the cell turgid
7
Relate the structure of the following to their functions
• red blood cells – transport
• root hair cells – absorption
Specialized cells:
Cells may be specialized for a particular function. Their structure allows them to carry out this function .
Examples of specialized cells
Cell
Function
Adaption
Absorbs light energy for
photosynthesis
Packed with chloroplasts. Regular shaped,
closely packed cells form a continuous layer
for efficient absorption of sunlight.
Absorbs water and
mineral ions from the soil
Long 'finger-like' process with very thin
wall, which gives a large surface area.
Leaf cell
Root hair cell
8
Cell
Function
Adaption
Fertilizes an egg cell female gamete
The head contains genetic information and
an enzyme to help penetrate the egg cell
membrane. The middle section is packed
with mitochondria for energy. The tail moves
the sperm to the egg.
Contain hemoglobin to
carry oxygen to the cells.
Thin outer membrane to let oxygen diffuse
through easily. Shape increases the surface
area to allow more oxygen to be absorbed
efficiently. No nucleus, so the whole cell is
full of hemoglobin.
Sperm cell
Red blood cells
Nerve cells
To carry nerve impulses to
different parts of the

body
Long
To join with male cell, and
then to provide food for

the new cell that's been
formed
Large

Female reproductive cell
(egg cell)
Connections at each end
Can carry electrical signals
Contains lots of cytoplasm
9
Calculate magnification and size of biological specimens using millimeters as units.
Practice:
1. using the images of the cells on pages 3 and 4 of these notes, calculate the actual size size of some
of the structures seen.
2. Search the internet for light and electron microscope images of various cells. If they have a scale
bar, print them and calculate the real size of the sample.
10
Know that cells are arranged in groups to form tissues.
tissue – a structure made from large numbers of one type of cell
Examples of tissues found in the human body
11
Examples of tissues found in a leaf
12