Disease, Immunity and Control

Diseases and Immunity

• Pathogen - disease-causing organism
• Transmissible disease - a disease in which the pathogen can be passed from one host to another
• Pathogens can be transmitted through direct contact (blood and body fluids) or indirectly(contaminated surfaces, food, animals, and air)
• Body has natural defenses against pathogens
• Skin prevents pathogen from entering. When broken, blood clots stop pathogens from entering
• Nose hairs filter pathogen contained particles
• Mucus traps bacteria in the airway. Swept to the back of the throat to be swallowed, rather than entering the lungs
• Stomach acid (hydrochloric acid) kills bacteria present in food
• White blood cells take in and digest pathogens via phagocytosis, while others produce chemicals called antibodies to incapacitate or directly kill pathogens

Controlling the Spread of Disease:

• Clean water supply is essential.
• Unsafe water can contain pathogens. Clean water promotes basic health and prevents waterborne diseases like cholera.
• Food should be hygienically prepared.
• Keep bacteria and viruses away from food by washing hands, wearing sanitary wear, and avoiding sneezing/coughing on food.
• Keep animals away from food sources.
• Don't keep foods at room temperature for extended periods to prevent bacterial growth, refrigeration slows it down and cooking kills it
• Keep raw meat away from other foods.
• Good personal hygiene reduces the risk of getting or spreading transmissible diseases, by making skin free of oils, dirt and sweat that provide breeding grounds for bacteria
• Regular washing with soap and shampoo , and Brushing teeth can help control harmful bacteria
• Waste disposal prevents bacteria from breeding in waste food
• Animals foraging in garbage and dangerous chemicals seeping into rubbish can be harmful
• Only licensed operators should add material to landfill sites
• Decomposing rubbish produces methane, needing ventilation to prevent explosions
• Full landfill sites should be covered with soil and grass Sewage treatment
• Sewage should be treated before entering rivers or the sea to avoid harming people and the environment
• Untreated sewage contains bacteria, microorganisms, likely pathogens and can transmit diseases like poliomyelitis and cholera

Active Immunity:

• Defence against a pathogen via antibody production
• Each pathogen has unique antigens with specific shapes
• Antibodies, proteins bind to antigens, directly destroying or marking for destruction by phagocytes.
• Specific antibodies complement specific antigens in shape.
• Active immunity follows infection or vaccination, where the body produces antibodies and memory cells, for disease protection
• A vaccine is a harmless preparation of dead or inactivated pathogens injected to induce an immune response
• Vaccination involves injecting weakened pathogens or antigens, stimulating lymphocytes to produce antibodies and memory cells for long-term immunity
• Vaccinations promote 'herd immunity', vaccinating enough individuals to protect the whole population since there are fewer places the measles virus can replicate

Passive Immunity:

• A short-term defence against pathogens through antibodies acquired from another individual
• Breast-feeding develops passive immunity in infants through disease-protecting antibodies transmitted from mother to infant.
• Memory cells aren't produced in passive immunity
• Active immunity develops after the body contacts pathogens, producing its own lymphocytes, antibodies, and memory cells through infection or injection of live/dead pathogens
• Antibodies in breast milk or transferred across the placenta, and Injected antibodies can also provide passive immunity

Cholera

• Cholera, is transmitted in contaminated water, is caused by a bacterium which produces a toxin causing secretion of chloride ions into the small intestine, causing osmotic movement of water into the gut, and resulting diarrhoea, dehydration and loss of ions from the blood

Coordination and Response

• Electrical impulses travel along neurones
• The mammalian nervous system has two systems
  • Central nervous system (CNS) - brain and spinal cord
  • Peripheral nervous system (PNS) - nerves outside brain and spinal cord
• The nervous system makes sense of our surroundings and coordinate and regulate body functions

Reflex Arc:

• A series of neurones transmitting electrical impulses from receptor to effector
• Order: receptor → sensory neurone → relay neurone → motor neurone → effector
• Sensory neurone carries impulses from sense organs to CNS
• Relay neurone (intermediate neurone) is inside the CNS, connecting sensory and motor neurones
• Motor neurones carry impulses from the CNS to effectors (muscles or glands)
• Stimulus - environmental change detected by sensory neurones
• Receptor - structure detecting stimulus, generating electrical impulse to CNS, e.g., skin
• Effector - structure responding to nervous system signal, resulting in action or behavior
• Reflex is involuntary, without brain coordination; awareness comes after completion
• Reflex action facilitates rapid integration and coordination of stimuli with responses of muscles and glands
• Voluntary action is conscious and coordinated by the brain
• Involuntary action happens without conscious thought, therefore the brain isn't needed to coordinate the response

Synapse:

• Junction between two neurones
• Synaptic gap is the tiny gap at the synapse
• Vesicles are small vacuoles
• Neurotransmitter is a chemical stored in vesicles released to diffuse, setting up electrical impulses
• Receptor proteins bind neurotransmitters at the synapse
• An impulse stimulates neurotransmitter release from vesicles into gap, which then diffuse
• Neurotransmitter molecules then bind with receptor proteins on the next neurone
• An impulse is then stimulated in the next neurone, and Synapses ensure one-way impulse travel

Sense Organs

• Respond to light, sound, touch, temperature, and chemicals
• Cornea refracts light
• Iris controls light entering the pupil
• Lens focuses light on the retina
• Retina contains light receptors, sensitive to different colors
• Optic nerve carries impulses to the brain
• The pupil reflex is an automatic response to a change in light intensity, the receptors are in the retina, and the effector is the muscles in the iris
• Accommodation is the eyes function that helps it view near and distant objects When an object is near:
  • Ciliary muscles contract, and suspensory ligaments are relaxed
  • The shape of the lens is thicker
  • Refraction of light by lens is more, to focus on the near object. When an object is far away:
  • Ciliary muscles relax, and suspensory ligaments are pulled tight
  • The lens becomes thinner
• 2 types of retina receptor cells: Rods for dim light night vision, and Cones for bright light color vision of 3 types (red, green, blue)
  • Rods are all over the retina except at the blind spot, Cones are concentrated at the fovea
• Blind spot - area where optic nerve leaves, no photoreceptor cells there
• Fovea - part of retina helping see details/colors clearly, high concentration of cone cells which gives us sharp vision

Hormones

• Chemical substance, made by a gland, carried by blood, alters activity of organs
• The glands make hormones, collectively known as the endocrine system

Gland, Hormone, and Function:

• Adrenal gland secretes adrenaline, preparing the body for vigorous action
• Pancreas secretes insulin, reducing blood glucose, or glucagon increasing blood glucose
• Testis secretes testosterone, causing development of male secondary sexual characteristics
• Ovary secretes oestrogen, causing development of female secondary sexual characteristics, and helps in the control of the menstrual cycle
• Adrenaline, secreted during fight or flight causes:
• Increased breathing rate to deliver more glucose and oxygen to the muscles and other vital organs quickly
• Increased heart rate to deliver oxygen and glucose to the muscles and vital organs
• Increased pupil diameter to give the brain more information
• Adrenaline increases blood glucose concentration for respiration and heart rate for energy release
• The nervous system is made of up neurones, that transit electrical impulses, and act faster with results that last a short time
• The endocrine system is made of glands, that transmit hormones released into the blood plasma, has a slower more gradual response.

Homeostasis

• Homeostasis - the maintenance of a constant internal environment
• Insulin decreases blood glucose concentration → conditions in the body change from a set point → change detected → corrosive mechanisms activated → conditions returned to set point → corrective mechanisms switched off →
• Cells in the pancreas detect that the blood glucose concentration is outside its normal limits
  • If it has gone too high, they secrete insulin
  • If it has fallen too low, they secrete glucagon
• Negative feedback - a mechanism that detects a move away from the set point, and brings about actions that take the value back towards the set point
  • There's a set point - a normal level that the system tries to maintain
  • There is a 'measuring device' that keeps track of whether the level is within range of the set point
  • If the level goes outside the set point, this triggers events to happen that bring the level back into line again
• Type 1 diabetes is caused insufficient insulin secreted by the pancreas, and can be controlled by;
  • Regular blood glucose checks , eating habits adapted to sport with carbohydrates for energy, and insulin injections
• The brain controls regulation and has has receptors sensitive to blood temperature, nerve impulses are sent from effectors in the skins temperature receptors

Thermoregulation

• When we are hot
  • Sweat glands secret liquids that becomes water vapor to cools skin by evaporation
  • Hairs lie flat against the skin, allowing air to freely circulate. Increases heat transfer to the environment by radiation
• When we are cold
  • Skeletal muscles contract rapidly when we shiver, and some energy is released as heat
  • Erect hairs trap a layer of air around the skin and act as an insulator to prevent heat loss
  • Fatty tissue acts as a layer of insulation to prevent too much body heat being lost through the skin
• Vasodilation, when we feel hot, arterioles widen to increases heat loss by radiation cooling the body down
• Vasoconstriction, arterioles narrow, slowing blood flow and reducing heat loss

Plant tropic responses

• Gravitropism - a response in which parts of a plant grow towards or away from gravity
• Phototropism - a response in which parts of a plant grow towards or away from the direction of a light source
  • Shoots normally grow towards light, they are positively phototropic
  • Roots respond to light, but grow away from light
  • Shoots grow away from gravity (negatively gravitropic)
  • Roots grow toward gravity (positively gravitropic)
• Plants control growth chemically with auxins Plants Hormones Called Auxins
  • Auxins control the direction of plant growth
  • Auxins are made in the shoot tip
  • Auxins promote cell division and cell elongation
  • Auxin diffuses throughout the plant from the shoot tip
  • Auxins respond to light and gravity

Excretion

• Excretion in humans removes;
• Carbon dioxide through lungs, urea and excess water ions through kidneys
• Excretion - the removal of waste substances of metabolic reactions, toxic materials and substances in excess of requirement
• Waste substances that need to be removed from the blood: urea, excess hormones, excess water, creatinine, ammonia, uric acid, excess salts/ions
• Nephrons have many functions:
• Ultrafiltration occurs when pressure in the glomerulus in the kidney capsule forces fluid of water, glucose, urea, ions intro nephrons
  • The kidney is responsible for selective reabsorption.
  • Nephron reabsorbs all glucose some ions and most water but no urea
  • What's left of the filtrate forms urine, which is made of urea, excess ions, and excess water
• Assimilation is where digested food molecules converted to molecules for the body to use. It takes place in the liver
• Excess amino acids in the liver are brocken down and can't be stored through deamination
• Deamination - the removal of the nitrogen-containing part of the amino acids to form urea
  • Urea is formed in the liver from excess amino acids
  • Urea dissolves in the blood and is taken to the kidney to be excreted
  • It is very important for urea to be excreted from th body

Asexual reproduction

• Asexual reproduction is a process resulting in the production if genetically identical offspring from one parent
• Bacteria reproduce exact clones of themselves through Binary ffission
• Some plants have underground storages that become next years plants, such as bulbs or tubers
• Some plants grow side shoots (runner) to produce separate tiny plantlets
• Advantages of reproduction in plants:
• wild species allows rapid population growth and crop plants allows crops to be produced with desired characteristes
• Disadvantages of reproduction in plants:
• Wild species has limited genetic variation and crops plants can be diseased

Sexual reproduction

• Sexual reproduction is is the fusion of 2 gametes that creates a zygote to produce genetically different offspring
• Fertilization - the fusion of nuclei of gametes
• Gametes are haploid cells and the nucleus of a zygote is diploid
• Advantages of sexual reproduction:
• Wild species have survival chance.
• Crop plants allow variation in genetic resistance
• Disadvantages of sexual reproduction in plants:
• Wild requires both mating partners
• Crop is a slow reproduction rate, and require more resources

Structure of flower

• Sepal - protects unopened flower
• Petals - brightly coloured in insect-pollinated flowers to attract insects
• Anther - makes and releases pollen
• Filaments - supports anther
• Stigma - sticky top of the female part of the flower which collects pollen grains
• Style - a tube that connects the stigma and ovary
• Ovary - contains the ovules
• Ovule - structures inside the ovary that contains the female gametes In a wind pollinated flower there are:
  • Anthers and stigmas hang outside to be blown away and caught by the wind

Pollination

• Insect-pollinated flowers produce larger, heavier pollen grains that contain spikes or hooks
• Wind-pollinated flowers produce small, lightweight pollen grains that can be caught and carried by the wind
• Pollination - the transfer of pollen grains from anther to a stigma
• Self-pollination - the transfer of pollen grains from the anther of a flower to the stigma of the same flower or a different flower on the same plant
• Cross-pollination - the transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species