Cell Structure

From ZuluNotes - Free Leaving Cert Notes

Diagram of a typical eukaryotic cell, showing subcellular components. Organelles: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles

Cell Membrane

Structure:The cell membrane is the very thin (7nm) outer layer of the cell. It's a thin unit membrane, the structure is layed out in the fluid-mosaic model. Functions include;

1. Provides shape and support for the cell
2. Acts as a selectively permeable barrier
3. Regulates the internal environment for optimal metabolism

Cell Wall

The cell wall is a non-living structure found only in plants. It is made of cellulose and is fully permeable. It's Primary Function is strength and support.

Middle Lamella

• Function:Cements cells together
• Contains Pectin

Nucleus

The nucleus is the control centre of the cell

Structure

It is a sac like structure surrounded by nuclear membrane which contains pores to allow material exchange with the cytoplasm

Function

1. Maintains Cell activities
2. Cell division (mitosis and meiosis)
3. Contains genetic information in the form of DNA

Nuclelus

Makes RNA (ribonucleic acid)

Cytoplasm

The watery gel in which the organelles are suspended, such as those listed below;

Mitochondria

Simplified structure of mitochondrion

• The powerhouse of the cell
• A large number of mitochondria are found in cells with high energy demand, such as the liver and muscle in animals and the shoot and root tips in plants

Structure

The mitochondrion consists of an outer and inner membrane. The inner membrane is folded. These foldings are known as cristae on the surface of which are found enzymes essential for respiration

Ribosomes

• Function: Protein Synthesis
• Ribosomes are made of RNA, and are present in large numbers in cells involved in protein synthesis, eg. the liver and pancreas

Endoplasmic Reticulum

This is the transport system for the cell. There are two types, the rough endoplasmic eticulum and smooth endoplasmic reticulum, The rough endoplasmic reticulum has ribosomes attached to it, whereas the smooth one does not.

• Functions of the rough endoplasmic reticulum:

1. Transport of protein from the ribosome
2. Transport of materials from inside to outside the cell

Plastids

The internal structure of a chloroplast, with a granal stack of thylakoids circled. Click to enlarge

Plastids are found only in plant cells only. They are divided into 3 types:

1. Luceoplasts - Used in starch storage
2. Chromoplasts - Provide pigment colouring
3. Chloroplasts - Used in photosynthesis

The structure of the chloroplast is often examined in the leaving cert and it's important to know how to label it.

Lysosomes

Lysosomes are saclike structures bound by a single membrane. They contain powerfull enzymes capable of digesting other organelles. Their functions include;

1. The breakdown of complex chemicals, eg. Protein and Nucleci acid
2. Distruction of worn out ogranelles, eg. Mitochondria
3. Helps disintegration of dead cells, eg. In a tadpole's growth to a frog

Centriole

These are mostly in animal cells, but also in some plant cells. They are absent in the flowering plant It lies close to the nucleus. There are two in each animal cell. Their main function is the formation of spindle fibres in cell division

Centrosome

The centrosome is the area of the cytoplasm containing the centrioles, i.e. close to the nucleus. It is only present only in animal cells and primitive plant cells.

Golgi Apparatus

This is a stack of very flattened membrane sacs called cisternae. Mainly in secretion cells, such as goblet cells. The main functions are:

1. Synthesis of materials, such as proteins and carbohydrates
2. An assembly area for materials to gather then be released from the cell