cell division

Chromosomes are structures located in the nucleus of the cell. They are made of DNA and protein. Chromosomes are long thin threads called chromatin until cell division occurs. Then they become visible as rod-like chromosomes. Chromosomes are composed of genes. All the genes of an organism make up the organism’s genome. Genes control the physical characteristics of a species. All organisms of the same species contain the same number of chromosomes in their nuclei.
HAPLOID AND DIPLOID CELLS

          Haploid cells contain 1 set of chromosomes in their nuclei. Diploid cells contain 2 sets of chromosomes in their nuclei. The human species contain 46 chromosomes in their nuclei. This is the diploid (2n) number. The sex cells of the species have 23 chromosomes in their nuclei. This is the haploid (n) number. When fertilisation takes place the 23 chromosomes (n) from the father (called Paternal chromosomes) and the 23 chromosomes (n) from the mother (called the Maternal chromosomes) combine to form the diploid (2n=46) number of chromosomes in the fertilised egg cell.
THE STAGES OF THE CELL CYCLE

INTERPHASE This is the part of the cell’s life process when it does not divide. In this phase the cell grows, proteins and enzymes are made, and it increases the number of cytoplasmic organelles. Near the end of interphase chromosome duplication occurs. When this occurs the single strand  chromosome becomes a double strand. Each strand has identical genes.
MITOSIS-DIVISION OF THE NUCLEUS:Mitosis is the division of the nucleus. Two daughter nuclei, genetically identical the original nucleus, are formed. The 2 cells formed by mitosis are called daughter cells.
STAGES OF MITOSIS
PROPHASE As seen on the diagram below, the chromatin condenses forming chromosomes. Each chromosome is composed of two identical sister chromatids connected at the centromere. At this stage the nucleolus and the nuclear membrane break down and the spindle fibres form.

METAPHASE

As seen on the diagram below, the chromosomes line up along the middle of the cell. Each chromosome is connected to both sides of the cell by spindle fibres attached to the centromeres.

ANAPHASE As seen on the diagram below, the spindle fibres shorten (contract) and split the pair of chromosomes at the centromeres. The 2 sets of chromosomes are pulled to the opposite sides (poles) of the cell.

TELOPHASE As seen on the diagram below, each chromosome group becomes a nucleus when a nuclear membrane is formed around it. The chromosomes uncoil to become chromatin and the nucleolus reforms. 

MEIOSIS

A human body cell contains 23 pairs of chromosomes. The gametes - sperm or eggs - contain half this number of chromosomes, which is why meiosis is sometimes called 'reduction division'. (For more on chromosomes go to DNA and genes)

Before meiosis begins, the chromosomes are copied exactly. The DNA of each chromosome is replicated to form two chromatids. They then arrange themselves into homologous pairs (both coding for the same characteristics), and prepare for cell division. At this point maternal and paternal chromatids can exchange bits of DNA to recombine their genetic material and increase the potential for variation.

The homologous pairs of chromosomes then separate and move to the poles of the parent nucleus. For each of the 23 pairs there is a 50-50 chance as to which pole the paternal or maternal pair of chromatids goes. With over 8 million possibilities there are many opportunities for variation.

The nucleus now divides to form two daughter nuclei, each with a mixture of paternal and maternal chromosomes but with half the full complement of genetic material (and no pairs at all). This division is called Meiosis 1.

Finally the two daughter nuclei themselves divide to form gametes. This second division - Meiosis 2 - works just like mitosis. The chromosomes (really pairs of chromatids) split apart to form the genetic material of the four new cells. The end result is four sex cells each with a complete but single set of 23 chromosomes.

On fertilisation the nuclei of the sperm and the egg join to form a new nucleus, called the zygote. The zygote contains 23 pairs of chromosomes - 23 single chromosomes from the sperm, and 23 single chromosomes from the egg.
The Significance if mitosis:

1. it produces two identical daughter cells that have the same number of chromosomes
2. genetic information on the chromosomes are identical
3. some organisms can reproduce asexually by mitosis. (bacteria)
4. growth and repair

The significance of meiosis:

1. meiosis reduces the chromosome number in the cell by half
2. chromosome diploid number is restored on fertilisation
3. reproduction in some organisms, production of gametes

The Respiratory System

The Respiratory System

• Respiration

 

The respiratory system allows intake of oxygen to, and removal of carbon dioxide from the body via the lungs
The intake of oxygen and expulsion of carbon dioxide is known as gaseous exchange
Air is taken in through the mouth. It passes through the pharynx and larynx to the trachea
The trachea is kept open by rings of cartilage
The trachea splits into two bronchi that lead into each lung. The bronchi split into bronchioles which eventually end in air sacs called alveoli

• Alveoli are surrounded by capillaries. Gaseous exchange of carbon dioxide and oxygen take place in the alveoli when CO2 pass from the capillaries to the alveoli and O2 passes from the alveoli to the capillaries.


• The lungs are protected by the rib cage. The diaphragm lies below the lungs and moves downwards to allow the lungs to expand when an animal inhales air

The Skeleton

The Skeleton

• Functions of the skeleton
  Support
  – to give the body shape and support soft tissues
  Protection
  –some organs such as the brain, heart and lungs are protected by the skeleton
  Movement
  –muscles are attached to bone
  Mineral storage
  Production of red blood cells


• Structure of Bone
  Joint
  –A place where two or more bones meet
  Cartilage
  –A layer of tissue found on bones between joints which reduces friction
  Spongy bone
  –Responsible for production of red blood cells
  Medullary cavity
  –Produces white blood cells
  Compact bone
  – The outer layer of bone which is hard


• Connective Tissue
  Adipose tissue
  – Its main function is to store fat. It is also used for insulation
  Tendons
  – Connect muscle to bone. Inelastic fibers made of collagen
  Ligaments
  – Connect two bones together at a joint. Also made of collagen
  Muscular tissue
  –Muscles cause movement in the body when they contract


• Muscle Types
  Skeletal muscle
  –Voluntary muscle attached to bones
  –It is under conscious control
  –Example: muscles in legs
  Smooth muscle
  –Involuntary muscle that lines internal organs such as the oesophagus
  Cardiac muscle
  –Involuntary muscle that does not fatigue
  –Found in the heart

The Nervous System and endocrine

• The Nervous System

The nervous system in vertebrate animals consists of two parts:
–Central Nervous System (CNS)
–Peripheral Nervous System (PNS)
The central nervous system consists of
–The brain
–The spinal cord
The peripheral nervous system consists of
–Sensory nerves
–Motor nerves
A nerve cell is called a neuron.

• The Nervous System
  This allows an animal to detect what is going on in the world around it.
  It includes the brain, the spinal chord and the nerve cells.
  The nervous system controls receptors such as the eye and the ear and it also control the effectors the most important of which are muscles.


• The Endochrine System


• The Endochrine System


• 


• This is the hormone system in the body.
  Hormones are produced in very small quantities, transported by the circulatory system to specific parts of the body, where they can stimulate or inhibit actions in the target organ or tissue.
  Hormones are produced in many parts of the body e.g. the pituitary gland, the thyroid glands, the parathyroid glands, the pancreas, the adrenal glands and the gonads.


• Milk Let-Down
  External factors such as the sight or sound of a calf or entering the milking parlour and being having teats rubbed.
  This sends a message to the brain which cause the hormone oxytocin to be produced by the pituitary gland.
  This message is carried in the blood to the udder causing milk alveoli to contract releasing milk.


• Endocrine Glands
  The pituitary gland is located at the base of the brain.
  Some of the hormones produced by the pituitary are growth hormone, prolactin, luteinising hormone (LH), follicle stimulating hormone (FSH) and oxytocin.
  Oxytocin is responsible for milk let down and contractions during birth.


• Thyroid glands
  –Located in the neck and produce thyroxine which regulates metabolism in the body and is responsible for growth
  Parathyroid glands
  –Located on the surface of the thyroid glands. They release parathyroid hormone which regulates calcium levels in the bones and blood.
  The Pancreas
  –Secretes insulin into the bloodstream when there are high levels of glucose in the body. The liver and muscle cells take up the glucose. Glucose is stored as glycogen in the liver.
  Adrenal glands
  –Produce adrenalin when the body is under stress.


• Sex Hormones
  Androgens are hormones responsible for male sex characteristics and are produced in the testis. Testosterone is an androgen
  Freemartin condition occurs in twin calves where one is male and the other is female. Hormones pass from the male to the female in the womb leaving the female infertile
  Ovaries secrete oestrogen and progesterone.
  Oestrogen promotes the sex characteristics in females.
  Progesterone allows for the growth of the uterus during gestation.

The Kidney and Urine Production

The Kidney and Urine Production

• The Kidney and Urine Production
  Blood arrives in the kidneys through the renal artery and leaves through the renal vein.
  Blood is filtered in the kidney, it removes harmful compounds and excess salts.
  The amount of water in the blood is also controlled
  Urine is formed in the kidney and passes to the bladder through the ureter.
  Urine leaves the bladder through the urethra.


• 


• Structure of the Kidney
  The kidney consists of tubules called nephrons.
  Nephrons are located in the cortex of the kidney.
  The Loop of Henle and Bowman’s Capsule are parts of the nephron.

Digestive Systems

Digestive Systems

• Mammalian Teeth
  Mammals have different teeth depending on what they eat.
  Herbivores have incisors for biting and premolars and molars for chewing grass.
  Carnivores have very large canines for ripping and tearing meat.
  Omnivores have a mixture of all teeth.

Foods
Chemicals found in foods include carbohydrates, fats, proteins, vitamins, minerals and water.
During digestion these foods are broken down into their different chemical components.
These chemicals are broken down further and absorbed.

• The Digestive System

 

The digestive system includes:
–Ingestion – taking in food.
–Digestion – breaking down food.
–Absorption – absorbing the nutrients.
–Assimilation – using the food.
–Egestion – eliminating the undigested food.

• Ingestion
  Physical and chemical digestion occurs in the mouth.
  When animals see or smell food they produce saliva from 3 pairs of salivary glands in the mouth.
  Saliva contains a slimy lubricating substance called mucus and an enzyme salivary amylase that breaks starch down to maltose.
  This mixing of food with saliva is called mastication and results in a bolus being formed which is swallowed.


• The Oesophagus
  food passes down a long tube called the oesophagus to the stomach.
  Rhythmical contractions of the muscles called peristalsis propel the bolus along.
  Birds have a special storage organ at the base of the oesophagus called the crop.


• The Birds Stomach


• 
  Part of the stomach of a bird is called the gizzard and it contains grit which the bird has swallowed.
  This grit along with muscle movement grinds hard foods such as cereal grains.


• Rabbit and Pig Stomachs


• 
  There is only one chamber in these stomachs and so they are called monogastrics.
  Digestive juices are produced such as hydrochloric acid, pepsin and rennin.
  Rennin is very important in young animals as it digests milk protein.
  Food enters the stomach through the cardiac sphincter and leaves through the pyloric sphincter.


• Digesting Cellulose
  Cellulose is a valuable food source if it can be digested.
  Some animals are able to digest cellulose by culturing bacteria, that live in their digestive system, and digest the cellulose for them.
  One of these groups have normal stomachs and long intestines with micro organisms in the hind gut. They are called hind-gut fermenters e.g. rabbits and horses.
  The second group have a specialised stomach with four chambers and are called ruminants e.g. sheep and cows


• Herbivores with monogastric stomachs ferment their food in the large intestine and the appendix.
  This fermentation (anaerobic respiration) digests the cellulose.


• The Ruminant Stomach


• 
  The stomach consists of four chambers:
  –The rumen – contains anaerobic bacteria and protozoa that digest cellulose. Ruminants also digest some of the micro organisms and get protein from them.
  –The reticulum – has a honeycomb wall and digests food further before it is passed back to the mouth for further mastication.
  –The omasum – cud enters here and water is squeezed out and absorbed, solids pass to fourth chamber.
  –The abomasum – like the normal stomach of a monogastric where digestive juices are produced. Calves send milk straight to the abomasum where it is digested by rennin.


• The Small Intestine
  The first part of the small intestine is called the duodenum.
  Bile, produced in the liver, is added to food here and helps break down fat.
  Pancreatic juices, produced in the pancreas, contains a number of enzymes including pancreatic amylase that breaks down starch.
  Pancreatic juices are also added in the duodenum and further break down the food.


• Further along the small intestine intestinal juice, which contains the enzymes sucrase (breaks down sucrose) and lactase (breaks down lactose), are added.
  The internal surface of the small intestine is called the ileum. It has villi that increase its surface area and help absorption of nutrients


• 


• The Liver: Functions
  Production of bile to emulsify fats and lipids
  Storage of glucose in the form of glycogen.
  Storage of Vitamins A,D,E,K
  The breakdown of toxic substances
  –Ammonia is converted to urea
  The breakdown of red blood cells
  Temperature regulation

Spring Barley

Spring Barley

• 1. Importance – Most widely grown cereal either for feeding or malting.
  2. Soil Type – Brown earths and grey brown pozolics. Deep sandy loams. pH 6.5 – 7. Dry weather for harvest.
  3. Seed Bed Preparation – plough in autumn to improve structure and harrow in spring to produce a fine seedbed.
  4. Seed – use Dept. of Ag. Certified seed choosing variety from Recommended List to ensure good crop e.g. Quench
  5. Sowing – sow as early as weather permits (March) with combine drill at a rate of 125-140kg/ha. Tillering will ensure 900 ears/m2. Roll seedbed.
  6. Use of Fertiliser – Apply a compound such as 10:10:20 with combine drill. N requirement depends on previous cropping history, soil type, rainfall and variety. P and K requirement depends on soil test.
  7. Disease & Pest Control – wireworms and smut are controlled by seed treatment. Mildew, rust and BYDV can be controlled by spraying crop (e.g. of spray = Bravo). Crop rotation and certified seed will reduce risk of attack.
  8. Weed Control – Weeds compete for moisture and nutrients and seeds can contaminate grain. Use crop rotation and stubble cleaning. Identify weed and use selective herbicide. Spray early when weed soft.
  9. Harvesting – Harvest when grain is dry and hard and moisture content is as low as possible. Straw dry and bleached and ear lies parallel to stem (usually August). Use combine harvester with all parts set correctly to minimise losses. Good yield 7-8 t/ha.
  10. Storage – Main source of damage is sprouting and attack by bacteria, fungi and insects. Dry the grain to 14% moisture to stop the above. Where grain is kept for feeding on farm use acid treatment which kills grain to prevent germination and stops bacterial attack.