'Prokaryotic' is a term used to describe cells of organisms such as bacteria that do not contain a nucleus.
Prokaryotae Kingdom contains prokaryotic organisms such as bacteria and cyanobacteria.
- single-celled organisms
- cells do not have nuclei
- DNA is in circular strands found in the cytoplasm and is not associated w/ proteins
- relatively few organelles found in their cytoplasm
- no membrane-bound organelles
'Eukaryotic' is a term used to describe cells that contain a nucleus. Animals and plants are eukaryotes and therefore have cells containing nuclei.
'Eukaryotae' - An organism with eukaryotic cells.
Similarities and Difference between Pro/Eukaryotes
Prokaryotes | Eukaryotes
- both contain nucleic material
- both have ribosomes
- both have a cell surface membrane
- Eukaryotic cells have a mean diamter of 10-100µm // prokaryotic cells have a mean diameter of less than 2µm
- Eukaryotic cells have many membrane-bound organelles such as mitochondria // Prokaryotic cells have few organelles and none of them are membrane-bound
- Eukaryotic cells have large ribosomes, prokaryotes have small ribosomes.
- Eukaryotes have linear DNA wrapped around proteins, found in a nucleus whereas prokaryotes have circular DNA which is not associated with any proteins and they don't have a nucleus.
- Eurkaryotic cells: Animal cells have no cell wall, plants have cellulose cell wall and fungi have chitin cell wall. Prokaryotes only have peptidoglycan (a polysccharide and polypeptide combined) cell wall (no cellulose or chitin cell wall)
NEVER TRUST A FUNGI CELL THEY'RE ALWAYS CHITIN THEMSELVES.
- Nucleolus - Dense body within the nucleus where ribosomes are made. All the chromosomes in the nucleus place their genes to make ribosomes in this area and as a result of all the proteins, the nucleolus appears darker when stained.
- Nucleus - Enclosed by an envelope composed of a double membrane perforated by pores. Contains choromosomes and a nucleolus. The DNA in chromosomes contains genes that control the synthesis of proteins.
- Ribosomes - Made of RNA and protein. Found free in the cytoplasm or attached to rER. They are the site of protein synthesis.
- Vesicle - Fluid-filled sac in the cytoplasm, surrounded by a single membrane. Transports substances in and out of the cell via the cell surface membrane and between organelles. Formed by the golgi apparatus or ER or at the cell surface.
- Rough ER - A system of interconnect, membrane-bound, flattened sacs. Ribosomes are attached to the outer surface. Proteins made by these ribosomes are transported through the rER to other parts of the cell.
- Golgi body - Stacks of flattened, membrane-bound sacs, formed by fusion of vesicles from the ER. Modifies proteins and packages them in vesicles for transport. Makes lysosomes.
- Smooth ER - Like the rER but w/o ribosomes. Produces lipids and steroids e.g reproductive hormones.
- Mitochondria - The inner of its two membranes is folded to form finger-like projections called cristae. It is the site of the later stages of aerobic respiration. Converts chemical energy into ATP using oxygen.
Chloroplasts and mitochondria
Chloroplasts and mitochondria are thought to have been prokaryotes. They may have developed a mutualistic relationship with eukaryotes.
Chloroplasts give sugar and oxygen.
Mitochondria give ATP.
Eukaryotes give protection and a more constant environment.
Chloroplasts and mitochondria have DNA seperate to the eukaryotes that they inhibit. However, they have lost their ability to replicate themselves and rely partly on enzymes made by their hosts.
Cells and Organelles
Which organelles contain DNA?
- nucleus and nucleolus
Which organelles have a double membrane?
Movement of proteins through the cell
- Proteins are made at ribosomes; rER ribosomes make proteins which will be excreted or attached to the cell membrance, ribosomes free in the cytoplasm create proteins which remain in the cytoplasm.
- New proteins produced at the rER are folded and processed in the rER.
- Then they're transported from the ER to the Golgi Apparatus in vesicles.
- The golgi apparatus modifies proteins and packages them in vesicles for transport.
- The proteins are transported around the cell.
- Proteins can be intracellular or extracellular.
Cell Organisation Part 1
Similar cells -> Tissues -> Organs -> Organ systems
Tissues; tissues are a group of similar cells
- squamous epithelium tissue; single layer of flat cells found in the alveoli in the lungs. 'epithelium' is a lining or covering tissue.
- xylem tissue; xylem vessel and parenchyma; supports the plant and transports water around the plant.
Plant -> Leaf is an organ
- Lower epidermis - Contains stomata to allow for gas exchange
- Spongy mesophyll - has gaps to allow the movement of gases
- Palisade mesophyll - where photosynthesis occurs
- Xylem - carries water into leaf
- Phloem - carries sugar away from leaf
- Upper epidermis - covered in a waterproof waxy cuticle to reduce water loss.
Cell Organisation Part 2
Animal Organ -> Lungs
- Squamous epithelium tissue - surrounds the alveoli where gas exchange occurs
- Fibrous connective tissue - helps to force air back out of the lungs when exhaling
- Blood vessels - capillaries around the alveoli
Organs -> Organ systems
Organs work together to form organ systems - each system has a particular function.
e.g respiratory system is made up of all the cells, tissues and organs involved in breathing.
Stem cells are unspecialised cells.
The process by which cells become specialised is called differentiation.
Stem cells become specialised throughd differential gene expression.
- All stem cells contain the same genes, but not all of the genes are expressed.
- Under the right conditions, some genes are activated and other genes are inactivated.
- mRNA is only transcribed from active genes.
- mRNA from these active genes is then translated to produce proteins.
- The proteins determine the structure of the cell and the cell processes.
- Changes made to the cell by these proteins are hard to reverse.
Three types of stem cells
- Totipotent - can divide to produce all the specialised cells in an organism and extraembryonic cells. Thus can become a whole organism.
- Pluripotent - can divide to produce all the specialised cells but not extraembryonic cells.
- Multipotent - can divide to produce a limited range of specialised cells
Totipotency of stem cells can be demonstrated using plant cell tissue culture. All stem cells in plants are totipotent.
- A cell is removed from a growing area of a plant e.g the root or shoot.
- The cell is placed in a growth medium containing nutrients and growth hormones.
- The growth medium is sterile to prevent competition between the plant cell and microorganisms.
- The plant cell will grow and divide into a mass of unspecialised cells and if the conditions are suitable (e.g if the plant cells are givent the right hormones) the undifferentiated cells will become specialised.
- Eventually, the cells will grow and differentiate into a whole new plant.
Fertilisation in humans
Double fertilisation in plants
Double fertilisation in plants
- Pollen grain
- Pollen tube
- Tube nucleus
- Two sperm nuclei
- Digestive enzymes
- Embryo sac in the OVULE
- Endosperm - food store for mature seed
Cell cycle consists of cell growth and cell division.
Interphase > Mitosis.
In interphase DNA replication takes place and the cell organelles are also replicated. ATP content is increased (ATP provides the energy needed for cell division).
Mitosis occurs in 4 stages : PRAYER MAT
Prophase Chromosomes condense. The nuclear membrance breaks down and the chromosomes lie free in the cytoplasm. The centrioles move to opposite ends of the cell forming a network of protein fibres across it called the spindle.
Metaphase Chromosomes line up in the centre of the cell and attach to the spindle fibres at their centromeres.
Anaphase The chromosomes separate to form two sister chromatids. The spindle fibres contract pulling one chromatid to each side of the cell, centromere first.
Telophase One chromatid reaches each centromere. The DNA uncoils forming chromosomes again. Nuclear membranes form around each set of chromosomes. There are now two nuclei. The cytoplasm then divides "cleavage" and there are two daughter cells produced. Each daughter cell now enters interphase!
Meiosis - the production of gametes
In meiosis a cell in the testes or ovaries undergoes two rounds of division to produce four haploid cells.
- DNA replicates so there are two identical copies of each chromosome called chromatids.
- The DNA condenses to form double armed chromosomes consisting of two sister chromatids.
- Homologous chromosomes align in the centre of the cell.
- The cell divides, separating the homologous chromosomes, halving the number of chromosomes.
- In the second division the sister chromatids are separated.
- Four new cells that are genetically different from each other are produced.
Adaptations and evolution
Varition and adaptations
Adaptations are features of an organism which improve its chances of survival and reproduction.
There are three types of adaptations:
- Behavioural - ACTS
- Physiological - PROCESSES
- Anatomical - STRUCTURAL FEATURES
Taxonomy is the science of classification.
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