Lysosomes

• Tiny sacs filled with fluid containing enzymes

• Enable the cell to process its nutrients• Responsible for destroying the cell after it

has died• Main sites of digestion, that is the break-

down of structures, within cells

What is a Lysosome?

• Waste disposal system of the cell, therefore referred to as “suicide bags”

• Found in most eukaryotic cells, that is, in all animal cells and in certain insectivorous plants

Structure of Lysosomes• Spherical, small sacs• Outer surface is formed by a single membrane

which is; resistant to digestion prevents the release of enzymes which would

destroy cell membrane• Contains hydrolytic enzymes and work best in

an acidic environment• Contents of lysosomes are acidic

Function of Lysosomes

i. Digestion of ingested food Primary lysosome fuses with the food

vacuole forming secondary lysosome In the secondary lysosome, the enzymes are

released and the materials inside are digested

ii. Autophagy process A process which unwanted structures within

the cell such as worn-out organelles are engulfed and digested

iii. Act as important role in the defence system

Phagocytic vacuoles are formed by white blood cells when engulfing bacteria

The lysosomal enzymes released into these vacuoles rupture the cell walls of bacteria

iv. Autolysis Self-digestion of a cell through the release of

enzymes of lysosomes within the cellThis occurs after cells die or in some

differentiation process

Mitochondrion

What is a Mitochondrion?• Membrane-bound organelle found in most

eukaryotic cells• Acts as the “powerhouse of the cell”

generates most of the cell's supply of adenosine triphosphate (ATP) through the process of cellular respiration

Structure of Mitochondrion • Have different shapes and sizes• Generally rod-shaped • Has two membranes, a smooth outer membrane

and an inner membrane• The outer one being separated from inner by a

narrow fluid-filled space called the intermembrane space

• The inner membrane is folded extensively into shelves called cristae

Functions of Mitochondria Sites of cellular aerobic respirationThe matrix contains enzymes of the Krebs cycleThe highly folded cristae increase the surface

area for the electron transport chain reactions.The energy released is harnessed in the

synthesis of ATP for use by energy-consuming activities of the cell

DNA in the mitochondria enables the mitochondria to replicate during cell division

Chloroplasts

What is a Chloroplast?

• A type of organelle that contains chlorophyll and other photosynthesis pigments

• Site of photosynthesis in eukaryotic cells• Present in photosynthetic cells

Structure of Chloroplast• Large organelle • Biconvex, disc-shaped structure • Bounded by a double membrane. Two

membranes separated by a small intermembrane space

• A series of interconnecting flattened membrane-bounded sacs, called the thylakoids, are found in the stoma

• Thylakoid membranes May be stacked into grana Surrounded by the semi-fluid stroma. The

stroma contains the enzymes which catalyse light-independent reactions.

Contains the circular DNA, ribosomes, starch granules which act as temporary carbohydrate store, and lipid globules

Functions of ChloroplastsSite of photosynthesis The grana and thylakoid membrane provide

large surface areas for chlorophyll and accessory pigments to be located to trap light energy and carry out production of ATP and NADPH

The stroma contains enzymes to carry out light-independent (Calvin cycle) reaction and the production of high energy organic molecules, for example, sugar molecules