Bio Unit 2 notes (QCE)

Unit 2 Biology Notes

Homeostasis

Maintenance of the constant internal environment for the body in response to both internal and external conditions

The body regulates the following to maintain optimal levels:

Temp, pH, blood glucose, water levels

The maintenance of homeostasis is controlled by either nervous or endocrine system

The nervous system uses fast electrical impulses to respond to stimulus

The endocrine system uses chemical messages in the form of hormones to respond to stimulus  

Stimulus - change to the environment

Receptor – detects change

Control centre - Interprets change

Effector - corrects change

Response – solution

The main types of receptors are:

◦       Photoreceptors

◦       Thermoreceptors

◦       Chemoreceptors

◦       Mechanoreceptors

◦       Nociceptors

Photoreceptors

Photoreceptors are responsible for detecting light and are found in the eye

Chemoreceptors

Chemoreceptors are responsible for detecting chemicals.

Thermoreceptors  

Thermoreceptors detect changes in heat and are usually found under the skin

Mechanoreceptors

There are many different types of mechanoreceptors are they are responsible for detecting sound, touch, movement, gravity, and the position of the body.

Nociceptors

Responsible for detecting pain and are found in most body tissues

Negative feedback:

Responds to the stimulus to stabilise and restore the original/optimum state. The response produced, counteracts the effect of the original stimulus. E.g: thermoregulation

Positive feedback:

Responds to the stimulus to enhance or amplify the change. It exacerbates the change to move it further away from its equilibrium state. E.g: Childbirth

Nervous system

The control and coordination of the body with a complex network of neurons that carry electrical signals to and from the brain

Neurons are: specialised cells that enable rapid transmission of information between cells.

There are three classes of neurons:

Efferent (motor) neuron, Afferent (sensory) neuron, Interneuron

Sensory neurons

Transmit information gathered from sensory input from the environment to the cns for processing. 

Motor neurons

Transmit information from the central nervous system to the muscles and organs (effector cells) that carry out required functions.

Interneurons

Are neurons found exclusively in the cns and are responsible for enabling communicating between the motor and sensory neurons.

Hormones

Hormones are chemical messengers that are produced by an organism to regulate the activity of cells and organs.

Each hormone regulates and controls the activity of a specific target structure.

Hormones do not begin any new activities, instead they modify the current rates of existing processes.

There are two main types of hormones:

Water soluble hormones (Hydrophilic)
- Made from amino acids, Classed as peptide hormones, Bind to receptors on the surface of target cells
 

Fat soluble hormones (Hydrophobic)
- Made from lipids, Classed as steroid hormones, Bind to receptors inside the target cell

Types of hormones

Autocrine Paracrine Endocrine

Endocrine hormones travel long distances through the blood stream to reach target cells with complementary receptors

Hormone responses are much slower than nerve responses as they have to travel long distances via the blood. However, are long lasting.

Signal transduction

Reception, Transduction, Response

Up-regulation:

Process of increasing the response to a stimulus due to the increase in the number of receptors on the cells surface

Down-regulation:

Process of reducing the response to a stimulus by reducing In the number of receptors of the cell surface 

Thermoregulation

Endotherm and ectotherm

Endotherms generate most of the heat they need internally. Because of this, the internal body temperature of an endotherm is independent of the temperature of the environment.

Ectotherms body temperature mainly depends on external heat sources.

Organisms have an optimal range of internal temperature for optimal enzymic activity and therefore have a series of mechanisms to allow them to regulate this.

These mechanisms are:

  1. Structural Behavioural Physiological Homeostatic

Structural mechanisms

All endotherms have structures that help them to conserve or release heat:

-       Special body coverings (fur, feathers, blubber etc)

-       Large or small vascular body parts (size of body parts like ears, tails etc to help release or keep heat)

-       Brown adipose tissue (breaks down to release energy)

-       Increased number of mitochondria

Behavioural mechanisms

The main types of behavioural mechanisms include:

Kleptothermy
- The huddling together of organisms to share each other’s body heat

Torpor (hibernation)
- When an organism lowers its metabolic rate significantly to save energy

Osmoregulation

Osmoconformer: 

Animals in which their water balance is directly determined by their environment (isotonic to surroundings).

Osmoregulator:

Animals which maintain a constant internal water balance regardless of their surroundings.

Osmoregulation in humans is all controlled by the stimulus response system     stimulus – receptor – control center – effector – response

Osmoreceptors and hypothalamus

Osmoreceptors constantly monitor water levels in the blood
Changes in water concentration triggers the hypothalamus to give a response

Nephrons of the kidneys

Main location of active water control

Physiological and homeostatic features aiding osmoregulation

Nephron

  1. Proximal tubule:
    -     reabsorbs about 60% of the water back into the blood after filtration

  2. Loop of Henle:
    - Surrounding blood is hypertonic and water is absorbed due to osmosis

  3. Collecting duct:
    -     Final site of water regulation which is controlled by ADH.

•       Anti Diuretic Hormone

- When the hypothalamus receives messages from the osmoreceptors about water levels in the blood, which sends a message to the pituitary gland which releases ADH. ADH binds to the collecting duct increasing its permeability to water and increases water reabsorption.

Osmoregulation in Plants

Stomata

The exchange of water in plants occurs by diffusion through the stomata

The rate of water loss/osmoregulation is controlled by the stomata

During the day the stomata opens and during the night the stomata closes

Vacuole

The vacuole’s responsibility is to store water

Cuticle

The cuticle is a thick waxy layer covering the epidermis of the plant, its role is to reduce water loss through evaporation.

Homeostatic Responses – Abscisic Acid

ABA is a plant hormone

ABA can do the following:

Be produced in the roots to increase growth in dry soil, Control stomatal closure, reducing water loss in plants, Slows growth during winter to protect the plant

Hydrophytes

Aquatic plants are called hydrophytes.

They have the adaptation to save themselves from excessive water in freshwater environment:

  1. Have a large surface area (SA) with a large number of stomata on their upper surface.

  2. Thin waxy cuticles to prevent water retention is not needed

  3. Lower levels of ABA hormone

Mesophytes (middle)

Xerophytes

Plants living in a severely dry, terrestrial environment

They have following adaptations to reduce the rate of transpiration:

  1. Have small thick leaves. This reduces the SA and therefore the number of stomata.

  2. Extremely thick waxy cuticles to prevent water loss

  3. High levels of ABA hormone

Infectious vs Non infectious diseases

What is a disease?

A physiological abnormality or significant disruption in the “normal” health of an organism.

Infectious diseases

Are caused by another organism/organic agent that can be passed from one individual to another either directly or indirectly

Non infectious diseases

Non infectious diseases cannot be passed from 1 individual to another

The main types of non-infectious diseases are:

Genetic, Lifestyle/malnutrition - Diet, smoking, drinking, lack of nutrients

Environmental exposure - exposure to chemicals, pollution, radiation

Main pathogens which cause disease are:
- Prions Viruses Bacteria Protozoa  Fungus  Parasites

Virulence

The virulence of a pathogen refers to its ability to cause disease

Virulence depends on:

The number of infecting microorganisms (pathogens) , Route of entry into the body, Response of the host immune

Virulence factors:

Adhesion Invasion Capsules  Toxins   Obtaining nutrition from the host

Modes of disease transmission

Direct Contact:

Person-to-person transmission through touch.

Contact with Body Fluids:

Transmission through blood, saliva, or other fluids.

Contaminated Food/Water:

Ingestion of pathogens through food or water.

Disease-Specific Vectors

Transmission via organisms like mosquitoes, ticks

Immune response

The immune system is the specific response of the body to invasion by foreign antigens and removes it

An allergy is just the body’s natural immune response to a usually harmless environmental substance like pollen/food.

Antigen:

Any substance that causes the body to make antibodies and undergo an immune response eg: pathogens - chemicals

Antibody:

Are proteins that are produced by the immune system to protect against the unwanted antigens.  Each antibody is specific to each antigen.

Antibodies recognise the foreign toxins and removes them (ANTIBODIES ARE GOOD FOR YOUR BODY!)

1st line of defence – Non-specific physical and chemical barriers

Physical barriers (Skin, Hair), chemical barriers (Enzymes found in secretions)

Biological barriers (Non-pathogenic (good) bacteria found in skin, mouth, nose, stomach)

2nd line of defence – Non-specific immune system

White blood cells  - Inflammation - Fever 

The non-specific response are controlled by white blood cells (leucocytes). The 5 main types of white blood cells in the innate immune response: Macrophages, Neutrophils, Monocytes, Dendritic cells, Natural killer cells

3rd line of defence - Specific immune system

Antibodies
T- cells
B- cells

Inflammatory response

  1. If pathogens breach the first line of defence the injured cells release chemicals (cytokines) which bring white blood cells to the affected area. 

  2. The white blood cells release histamines (chemical) which causes vasodilatation, increasing the blood flow to the affected area (results to swelling and redness). 

  3. This increased blood flow to the area increases temperature which inhibits the growth of pathogens and inactivates the toxins they release.

  4. The increased blood flow also brings extra white blood cells to the area to undergo phagocytosis and kill the pathogens. 

5.      This inflammation response continues until the pathogen is eliminated

Third line of defence – specific

Immune response that keeps a record of past exposures to pathogens and learns

B cells

When a B-cell recognises a foreign antigen, it starts producing antibodies which are specific only to the shape of the specific antigen.

B cells recognise foreign antigens and start producing antibodies (the antigen only works with specific antibodies)

The B-cells then divide rapidly and produce many identical B-cells.
- Some form plasma cells B-cells which continue to produce and secrete the specific antibodies.
- Some form memory cells B-cells which persist long after the antigen has been removed and preventing reinfection in the future

T cells

•       When an antigen is discovered, it triggers the production of T-cells.

•       There are many types of T-cells:

  1. Cytotoxic (killer) T-cells – produce toxic substances that enter and kills the cells that have been invaded by a pathogen. (different to antibodies)

  2. Helper T-cells – help B-cells divide more rapidly (to create more antibodies)

  3. Suppressor T-cells – turn off the immune response and supress the production of antibodies when they are not needed

There are three main types of protection in plants:

Physical ,Chemical , Immune

Physical defence in plants

Waxy Cuticle , Cell Wall , Bark ,Thorns/hairs , Drooping leaves/leaf shape

Chemical defence in plants

Antimicrobial (antibiotics), Toxins

Immune response in plants

•       Basal resistance:
- Plant immediately fortifies itself against infection by becoming impenetrable (closing stomata)
- Releases chemicals (soponins, phytoalexins, defensins) which destroy the pathogen

•       Hypersensitive response:

- Limits pathogen spread through the plant and restricts it to the infected site by undergoing apoptosis (programmed cell death)

 

Controlling disease

Vaccine

You can become immune to a disease through vaccination. Vaccines are produced to target a specific pathogen.

Vaccines are made from:

Live pathogens that have been genetically altered so that they are weakened and are unable to cause disease.

Dead pathogens

mRNA which produces a protein specific to that pathogen and trigger an immune response.
(covid 19 vaccine)

5 factors that affect spreading of disease

  1. Pathogen features (persistence)
    - How long a pathogen can survive and replicate

  2. Method of transmission
    - Direct (person-to-person contact) OR Indirect (Food, water, air or vectors)

  3. Population density
    - How close people live. Diseases spread faster in denser populations.

  4. Movement of individuals
    - Movement patterns (travel, migration) affect disease spread by infecting induvial around the world

  5. Proportion of population immune
    - herd immunity

Herd immunity

If a significant proportion of the population is Immune to a disease, then any susceptible individuals are prevented from coming into contact with the pathogen.

If some of the population’s immune then susceptible individuals aren’t going to come into contact with pathogen.

As long as a certain percentage of the population is vaccinated then the disease would not be able to spread.

Useful in protecting the members of the population who cant be vaccinated – old, young, venerable immune systems.

If they are surrounded by people who are vaccinated then they have the protective bubble of the herd.