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Hey!

I know I haven't posted in a while, but I've just started my degree in Biology and Psychology and was wondering if anyone would be interested in me posting photos of some of my a level notes? 😊

#a level biology #a levels #biology #ocr alevel #ocr biology #year 12 #year 13 #college #science #alevel #ocr a level biology

Student's t-test for comparing means and calculating whether data is significant

#classification and evolution #module 4.3 #applying statistical techniques #student's t-test #a level biology

The evidence for natural selection and Variation

#the evidence for natural selection #variation #classification and evolution #module 4.3 #a level biology

Classification notes

#classification #a level biology #module 4.3 #classification and evolution

Chloroplasts

Structure: They are large organelles, typically 4-10 micrometers long. They are found only in plant cells and in some protoctists. They are surrounded by a double membrane or envelope. Chloroplasts contain loops of DNA and starch grains. Function: Chloroplasts are the site of photosynthesis. The first stage of photosynthesis, when light energy is trapped by chlorophyll and used to make ATP, occurs in the grana. Water is also spilt to supply hydrogen ions. The second stag,when hydrogen reduces carbon dioxide, using energy from ATP, to make carbohydrates, occurs in the stroma. Chloroplasts are abundant in leaf cells particularly the palisade mesophyll layer.

#cell structure #module 2.1 #the ultrastructure of eukaryotic cells: membrane-bound organelles #chloroplasts #a level biology

Mitochondria

(Singular: Mitochondrion) Structure: They are either spherical, rod-shaped or branched, and are typically 2-5 micrometers long. They are surrounded by two membranes with a fluid-filled space between them. The inner membrane is highly folded into cristae. The inner part part of the Mitochondrion is a fluid filled matrix.

Function: Mitochondria are the site of ATP production during aerobic respiration. They are self-replicating so more can be made if the cells energy needs increase. They are abundant in cells where much metabolic activity takes place, for example in liver cells and at synapses between neurones where neurotransmitter is synthesised and released.

#cell structure #module 2.1 #the ultrastructure of eukaryotic cells: membrane-bound organelles #mitochondria #a level biology

Golgi Apparatus

(Also called ‘Golgi body’) Structure: This consists of a stack of membrane-bound flattened sacs. Secretory vesicles bring materials to and from the Golgi apparatus.

Functions: Proteins are modified. This can be done by adding sugar molecules to make glycoproteins, adding lipid molecules to make lipoproteins, and being folded into their 3D shape. The proteins are packaged into vesicles that are pinched off and then either stored in the cell or moved to plasma membrane in order to be incorporated into the plans membrane, or exported outside the cell.

#cell structure #module 2.1 #the ultrastructure of eukaryotic cells: membrane-bound organelles #golgi apparatus #a level biology

Smooth endoplasmic reticulum

Structure: This is a system of membranes that contain fluid-filled cavities (cisternae) that are continuous with the nuclear envelope. There are no ribosomes on its surface.

Function: SER contains enzymes that catalyse reactions involved with lipid metabolism. This contains the synthesis of cholesterol, the synthesis of lipids or phospholipids needed by the cell, and the synthesis of steroid hormones. It is involved in absorption, synthesis and transport of lipids.

#cell structure #module 2.1 #the ultrastructure of eukaryotic cells: membrane-bound organelles #smooth endoplasmic reticulum #a level biology

Rough endoplasmic reticulum

Structure: It’s a system of membranes that contain fluid-filled cavities, known as cisternae, that are continuously with the nuclear membrane. It is coated with ribosomes.

Function: RER is the intracellular transport system as the cisternae form channels for transporting substances from one area of a cell to another. It provides a large surface area for ribosomes, which assemble amino acids into proteins. These proteins then actively pass through the membrane into the cisternae and are transported to the Golgi body for modification and packing.

#cell structure #module 2.1 #the ultrastructure of eukaryotic cells: membrane-bound organelles #rough endoplasmic reticulum #rer #a level biology

Nucleus, nuclear envelope and nucleolus

Structure: The nucleus is surrounded by a double membrane known as the nuclear envelope. There are pores in the nuclear envelope. The nucleolus does not have a membrane around it, and contains RNA.

Function: The nuclear envelope separates the contents of thr nucleus from the rest of the cell. In some regions the outer and inner nuclear membranes fuse together. At these points, some dissolved substances and ribosomes can pass through. The pore enable larger substances, like mRNA, to leave the nucleus. The nucleolus is where ribosomes are made. Chromosomes contain the organisms genes. The nucleus stores the organisms genome,is in control of the cell, transmits genetic information, and provides the instructions for protein synthesis.

#cell structure #module 2.1 #the ultrastructure of eukaryotic cells: membrane-bound organelles #nucleus #nuclear envelope #nucleolus #a level biology

Eukaryotic cells

All animal, plant, fungal and protoctist cells are eukaryotic. This means they have: - A nucleus surrounded by a nuclear envelope. - A nucleolus within the nucleus - Cytoplasm - A cytoskeleton - A plasma membrane - Membrane-bound organelles - Small vesicles -Ribosomes

#cell structure #module 2.1 #the ultrastructure of eukaryotic cells: membrane-bound organelles #eukaryotic cells #a level biology

Electron microscopes

Advantages: Very high resolution and magnification

Disadvantages: Very large Expensive Require a lot of skill and training to use Specimens have to be dead Metallic salt stains can be hazardous

#cell structure #module 2.1 #microscopes #a level biology

Scanning electron microscopes

Electrons bounce off the specimen to form an image of the surface.

It creates a 3D image with a magnification from x15 to x200,000.

The image is black and white, but computer software can be used to add false colour.

The specimen still has to be placed in a vacuum and is often coated with a fine film of metal.

#cell structure #module 2.1 #microscopes #a level biology

Transmission electron microscopes

The specimen has to be chemically fixed by the process of DEHYDRATION and STAINING.

The beam of electrons pass through the specimen, which is stained with metal salts. Some electrons pass through and are focused on the screen or photographic plate.

They form a 2D BLACK AND WHITE IMAGE. They can produce a magnification up to 2 MILLION TIMES.

#cell structure #module 2.1 #microscopes #a level biology

Laser scanning microscopes

(Aka: confocal micrpscopes)

They use laser light to scan an object point by point to create an image of the specimen displayed on a computer screen.

The images have a high resolution and high contrast.

These microscopes have depth selectivity and can focus on structures at different depths within a specimen.

They can be used to clearly observe whole living specimens, as well as cells.

#cell structure #module 2.1 #microscopes #a level biology

Optical microscopes (light microscopes)

Advantages: Cheap Portable Easy to use Use to study whole living specimens

Disadvantages: Limited resolution - 400-700nm so structures closer than 200nm will appear as one object

#cell structure #module 2.1 #microscopes #a level biology

Resolution

The clarity of an image produced by a microscope, which can be shown by distinguishing two points that are close together.

#cell structure #module 2.1 #microscopes #a level biology

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