biology 1

Eukaryotes and prokaryotes

venn diagram

Animal and plant cells

Most animal cells have the following parts: a nucleus cytoplasm a cell membrane mitochondria ribosomes. In addition to the parts found in animal cells, plant cells often have: chloroplasts a permanent vacuole filled with cell sap. Plant and algal cells also have a cell wall made of cellulose, which strengthens the cell.

animal cell specialisation

sperm cells

animal cell specialisation

muscle cells

animal cell specialisation

nerve cells

cell differentiation

Why differentiation is important - It allows organisms to: Develop different types of specialised cells. Form tissues, organs, and organ systems. Function efficiently — each cell type doing a specific role (e.g. red blood cells carry oxygen, muscle cells contract, root hair cells absorb water). During differentiation, a cell develops new sub-cellular structures (like mitochondria, chloroplasts, or a large vacuole). These structures help it carry out a specific function. When differentiation is complete, the cell is specialised. In animals: Most types of animal cells differentiate at an early stage of development (e.g. in embryos). After this, most animal cells lose the ability to differentiate. In adults, cell division mainly happens for repair and replacement of old or damaged cells. In plants: Many plant cells retain the ability to differentiate throughout life. This happens especially in meristems (regions of growth, like shoot and root tips).

microscopy

An electron microscope has much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures.

Culturing microorganisms

Bacteria multiply by simple cell division (binary fission) as often as once every 20 minutes if they have enough nutrients and a suitable temperature. Bacteria can be grown in a nutrient broth solution or as colonies on an agar gel plate. Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics. prep - Sterilise Petri dishes and culture medium Usually done in an autoclave (or heating) before use To kill any unwanted microorganisms that could contaminate the culture. - Sterilise the inoculating loop Pass it through a flame before transferring bacteria To kill microorganisms on the loop and avoid contamination. - Secure Petri dish lid with tape Use adhesive tape (not sealed all the way around) Prevents microbes from the air getting in, but still allows oxygen to enter (so no harmful anaerobic bacteria grow). - tore Petri dish upside down The lid faces downwards Prevents condensation from dripping onto the agar and spreading the microorganisms. - Incubate at 25°C (in school labs) Lower temperature than used in industry Reduces the risk of growing harmful pathogens that thrive at body temperature (37°C). Area=πr2

chromosomes

The nucleus of a cell contains chromosomes made of DNA molecules. Each chromosome carries a large number of genes. In body cells the chromosomes are normally found in pairs.

mitosis and the cell cycle

Cells divide in a series of stages called the cell cycle. Students should be able to describe the stages of the cell cycle, including mitosis. During the cell cycle the genetic material is doubled and then divided into two identical cells. Before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria. The DNA replicates to form two copies of each chromosome. In mitosis one set of chromosomes is pulled to each end of the cell and the nucleus divides. Finally the cytoplasm and cell membranes divide to form two identical cells. Cell division by mitosis is important in the growth and development of multicellular organisms.

stem cells

A stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells. Stem cells from adult bone marrow can form many types of cells including blood cells. Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant. Knowledge and understanding of stem cell techniques are not required. Treatment with stem cells may be able to help conditions such as diabetes and paralysis. In therapeutic cloning an embryo is produced with the same genes as the patient. Stem cells from the embryo are not rejected by the patient’s body so they may be used for medical treatment. The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections. Stem cells from meristems in plants can be used to produce clones of plants quickly and economically. Rare species can be cloned to protect from extinction. Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.

diffusion

Substances may move into and out of cells across the cell membranes via diffusion. Diffusion is the spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration. Some of the substances transported in and out of cells by diffusion are oxygen and carbon dioxide in gas exchange, and of the waste product urea from cells into the blood plasma for excretion in the kidney. Factors which affect the rate of diffusion are: - the difference in concentrations (concentration gradient) - the temperature - the surface area of the membrane. A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism. In multicellular organisms, surfaces and organ systems are specialised for exchanging materials. This is to allow sufficient molecules to be transported into and out of cells for the organism’s needs. The effectiveness of an exchange surface is increased by: - having a large surface area - a membrane that is thin, to provide a short diffusion path - (in animals) having an efficient blood supply - (in animals, for gaseous exchange) being ventilated

osmosis

Water may move across cell membranes via osmosis. Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

active transport

Active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient). This requires energy from respiration. Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil. Plants require ions for healthy growth. It also allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration. Sugar molecules are used for cell respiration