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SAMPLE 2 – ASSESSMENT CRITERIA AND LEARNING OUTCOMES
Human Biology RH3/3/AA/07G
4. Understand the importance of
homeostasis
5. Understand the nature of growth and
reproductive processes
6. Understand the role of the body
defences
4.1 Explain the roles of the nervous,
endocrine and urinary systems in
maintaining homeostasis
5.1 Explain the role of mitosis and
meiosis in growth and reproduction
5.2 Discuss the factors which influence
growth and reproduction
5.3 Explain the roles played by cell
multiplication, differentiation,
reorganisation and maturation in
growth and reproduction
6.1 Explain the role of primary and
secondary defence mechanisms
6.2 Discuss auto-immune diseases and
allergies
SAMPLE 2 – GRADING DESCRIPTORS AND COMPONENTS
GD1 – Understanding of the subject
Merit
1a) The student, student’s work or
performance:
Distinction
1a) The student, student’s work or
performance:
Demonstrates a very good grasp of the
relevant knowledge base
Demonstrates an excellent grasp of the
relevant knowledge base
GD7 – Quality
Merit
The student, student’s work or
performance:
a) Is structured in a way that is
generally logical and fluent
Distinction
The student, student’s work or
performance:
a) Is structured in a way that is
consistently logical and fluent
SAMPLE 2 – STUDENT WORK
1. Homeostasis in the nervous, endocrine and urinary systems
“Homeostasis is the maintenance of a constant internal environment within a living
organism” (Williams,G. 2000)
Homeostasis is the regulation of the internal environment of the body that takes
place through several complex biological processes. These processes operate
through the autonomic nervous system to neutralise changes that upset metabolic
equilibrium. Homeostasis controls internal conditions such as temperature, blood
pressure, water and electrolyte balance and respiration. (Marieb,E,Hoehn,K. 2007)
Each process or reaction has a desirable peak environment called the norm, where
influences such as an external influence can deviate away from the norm with the
body subsequently correcting this change; this is known as negative feedback. The
nervous and endocrine systems control homeostasis in the body through feedback
mechanisms involving various organs and organ systems, with the maintenance of
homeostasis being one of the most important functions of the endocrine system.
(Marieb,E,Hoehn,K. 2007)
Examples of negative feedback would be when blood pressure rises, the heart will
slow down, or if glucose levels are too high, the pancreas will then secrete insulin to
stimulate the absorption of glucose. Another feature of homeostasis is temperature
regulation by a complex system controlled by the hypothalamus which adjusts
breathing, metabolic rates, blood vessel dilation and blood sugar levels in response
to changes caused by factors including ambient temperature, hormones and
disease. (Williams,G. 2003)
The diagram below is a representation of negative feedback loop, showing how the
body sweats to help the body cool down. Once the body has cooled down, it stops
this process therefore returning the body back to its homeostatic state. This process
is regulated by the nervous system using three functions which detect the stimuli,
SAMPLE 2 – STUDENT WORK
process information about the stimuli then initiate a response, therefore maintaining
homeostasis. (Williams,G. 2003)
(Sbi.Weebly.com 2013)
A complex system of cycles and negative feedback is used by the endocrine system
to maintain homeostasis. Negative feedback regulates the secretion of relevant
hormones; secretion cycles are used to maintain physiological and homeostatic
control.
An example of how this happens is how it controls thyroid function which regulates
energy consumption, protein production and calcium in the blood. The hypothalamus
detects the inadequacy of thyroid hormones like thyroxine and triiodothyronine, and
releases hypothalamin which activates the anterior pituitary cells responsible for
secretion. The anterior pituitary releases thyrotropin; a thyroid-stimulating hormone
SAMPLE 2 – STUDENT WORK
which activates production of more thyroxine. If the hypothalamus detects excess
thyroid hormones, it takes corrective measures to restrict further production of these.
The hypothalamus is the region of the brain containing a control centre for many
autonomic nervous system functions. Its complex interaction with the pituitary gland
makes it an important part of the endocrine system and as a critical link between
these two control systems, the hypothalamus regulates homeostasis. Nervous and
hormonal pathways connect it with the pituitary, which stimulates to release various
hormones, as seen in the diagram below. Additionally, the hypothalamus influences
food intake, weight regulation, fluid intake and balance, thirst, body heat and the
sleep cycle.
(jeejeebhoy.ca 2010)
SAMPLE 2 – STUDENT WORK
Maintaining homeostasis is one of the most important functions of the endocrine
system, which comprises of a set of ductless glands that regulate the biological
processes of the body by producing and releasing hormones. The endocrine system
influences every cellular function within the body, with hormones and glands being
this systems foundation, which send and relay messages between different systems.
Many different hormones move through the bloodstream and are intuitively designed
to affect certain cells. (Marieb,E,Hoehn,K. 2007)
The endocrine system controls body systems and homeostasis by releasing
hormones into the bloodstream; neuron cell bodies of the hypothalamus produce
antidiuretic hormone (ADH) and oxytocin shown in the above diagram. These
hormones are transported along the axons to the axon terminals in the pituitary
posterior lobe. Both hormones are stored in the terminals until they are released into
the blood vascular network surrounding the posterior pituitary gland. Oxytocin is
controlled by positive feedback where the original stimulus is enhanced causing an
increased output. This triggers milk release from breast tissue and causes miscle
contractions in the uterus during labour. (Marieb,E,Hoehn,K. 2007)
ADH is controlled by negative feedback, and acts upon the kidney tubules to help
maintain a constant level of body water; this is called osmoregulation. This level is
accomplished by increasing the water re-absorption amount when body water levels
are low. The kidneys have a major role in homeostatic maintenance and are the
main organs of the urinary system, filtering nitrogenous waste products from the
blood as urea then excreted as urine; this is filtered through nephrons as seen in the
diagram below. This process occurs when waste products that are made in the
body’s cells during metabolic activity must be excreted to avoid a build-up of toxic
materials.
(Unckidneycenter.org 2014)
SAMPLE 2 – STUDENT WORK
Most filtration occurs in the glomerulus, where blood pressure forces in water, salt,
glucose, amino acids and urea. Proteins and blood are too large to cross the
membrane so remain in the blood. As the remaining fluid enters and flows through
the tubule, most of the water and nutrients are reabsorbed into the blood, with the
remaining concentrated fluid passing out as urine. (Fullick,A, et al. 2011)
The endocrine system is unique in that it uses glands and cells within organs that are
closely related to other body systems. The Endocrine System works with the nervous
system by sending hormones to cells and causing a physical reaction. These
hormones provide feedback to the brain and affect neural processing, which give the
body instructions on how and when to react to certain occurrences. The circulatory
System works as the transport system for endocrine information, sending hormones
throughout the body where they can be received by various organs and cells, then
put to use through bodily functions. (Biologyguide.net. 2014)
The Endocrine System also works with the digestive system through the pancreas,
which produces the hormone insulin. When carbohydrates are digested, they are
then transformed into sugars. The pancreas, which is also part of the endocrine
system, produces the hormone insulin to regulate how fast the sugars are
consequently broken down, therefore insulin regulates the amount of sugars in the
blood (blood glucose homeostasis). (Biologyguide.net. 2014)
2. Mitosis and meiosis in growth and reproduction
Cell division is essential for body growth, reproduction and growth, and is needed to
replace cells which become worn out and to repair damaged tissue, although the
new cells must hold the same genetic material in order to perform the same task.
These ‘parent’ cells divide and pass on their genetic material to the ‘daughter’ cells
For example, cells of the skin that continually wear away reproduce themselves
almost continuously. (Biology-online. 2014)
Each cell in the body has a nucleus which contains the inherited genetic material
(DNA) including instructions for making new cells, which are carried in the form of
genes. DNA molecules are composed of two strands of DNA coiled up into a double
helix, genes however are short sections of DNA controlling characteristics in the
body such as eye colour, and are grouped together to form chromosomes; each
person has 46 chromosomes arranged in 23 pairs. (Fullick,A, et at. 2011)
New cells are formed by the division of existing cells by either the process of mitosis
or meiosis.
SAMPLE 2 – STUDENT WORK
(davidsblogiisb.blogspot.co.uk
2011)
In mitosis, as seen in the above diagram, a parent cell produces two daughter cells
that are genetically identical, maintaining 46 chromosomes (2n) and are known as
diploid cells. As diploid cells contain the same hereditary information, this allows no
variation within the cell therefore increasing genetic stability. This form of cell division
occurs in human tissue growth and repair such as healing a cut in the skin, where
the tissue replaces the damaged cells with identical cells, thus enabling the same
function. (Williams,G.2003)
In meiosis, as seen in the above diagram, the parent cell produces four genetically
different cells which are known as haploid cells containing half the genetic material of
diploid cells (23 chromosomes, n), formed in a two stage process. The parent cell
divides to produce two daughter cells which subsequently divide again to produce
four daughter cells, therefore creating new genetic types resulting in genetic variety.
(Williams,G.2003)
SAMPLE 2 – STUDENT WORK
Gametes are male or female reproductive cells which are haploid cells, each
genetically different containing 23 chromosomes and produced by gametogenesis
within the gonads. This is important in the reproduction process so that when two
haploid cells are joined, the same number of chromosomes from the male and
female are given to form a diploid cell containing 46 chromosomes. In males,
spermatogenesis takes place to form sperm in the testes, whereas in females,
oogenesis takes place to form eggs in the ovaries. In reproduction, a haploid sperm
(n) and a haploid egg (n) fuse together during fertilisation to produce a diploid
fertilised egg (2n), which then rapidly divides many times by mitosis to grow
eventually into an embryo. (Fullick,A, et at. 2011)
The mixture of genetic information from two parents leads to genetic variety in the
offspring, which is advantageous in enabling a species to survive. Genetic variability
is a measure of the tendency of individual genotypes in a population to vary from one
another, whereas genetic diversity is the amount of variation seen in a particular
population. The variability of a trait describes how much that trait tends to vary in
response to environmental and genetic influences, which is important for biodiversity
as it enables a population to adapt to environmental changes and therefore making it
less prone to extinction. Variability is an important factor in evolution as it affects an
individual’s response to environmental changes therefore leading to differential
survival of organisms within a population due to natural selection of the most fit
variants. Genetic variability also underlies the differential susceptibility of organisms
to diseases and sensitivity to toxins or drugs. (Fullick,A, et at. 2011)
3. Multiplication, differentiation, reorganisation and maturation in cell growth
and reproduction
Cell multiplication
Cell multiplication is part the cell cycle, constantly replacing themselves with fresh
copies during mitosis. An example of cell multiplication would be when cells multiply
to repair damaged tissue. The phase of wound healing are the inflammatory phase,
the proliferation phase and the maturation phase.
The inflammatory phase is the body’s natural response to injury where the blood
vessels in the wound bed contract and a clot, known as haemostasis. The blood
vessels then dilate to allow essential cells such as antibodies, white blood cells,
growth factors, enzymes and nutrients to reach the wounded area, which leads to a
rise in exudate levels, so the surrounding skin needs to be observed for signs of
maceration. It is at this stage that the characteristic signs of inflammation can be
seen; erythema, heat, oedema, pain and functional disturbance.
During proliferation, the wound is repaired with new granulation tissue which is
comprised of collagen and extracellular matrix and into which a new network of blood
vessels develop. Healthy granulation tissue is dependent upon the fibroblast
receiving sufficient levels of oxygen and nutrients supplied by the blood vessels.
SAMPLE 2 – STUDENT WORK
Maturation is the final phase and occurs once the wound has closed, involving the
remodelling of collagen from type III to type I. Cellular activity reduces and the
number of blood vessels in the wounded area regress and decrease.
(Marieb,E,Hoehn,K.2007
Cell differentiation and reorganisation
The process of unspecialised embryonic stem cells becoming specialised cells
involves the stem cells both differentiating and then reorganising into areas of
specialised cells.
Embryonic differentiation is the process of development during which embryonic
cells specialize and create diverse tissue structures. The differentiation of cells
during embryogenesis is essential to cell, tissue, organ, and organism identity. Once
an egg is fertilized by a sperm, a zygote is formed, which then divides into multiple
cells triggering the beginning of embryonic differentiation. This zygotic division
produces blastomeres which later make up the hollow sphere known as the blastula,
where the cells go through reorganisation that define the structure of the embryo and
consequent organism. In this process, called gastrulation, three germ layers are
formed; the endoderm, mesoderm, and ectoderm. Cells reorganised in these three
layers will give rise to different parts of the organism. As the embryo continues to
mature, individual cells continue to differentiate. These differentiated cell types are
made from what were initially the same types of pluripotent embryonic cells.
Differentiation of cells in the embryo is brought about by both internal cellular factors
as well as extracellular factors that act on the cell from the outside. Regulative
development involves the interaction of adjacent cells, within what is known as
embryonic fields. The advantage of regulative development is the flexibility that it
confers to differentiation. For example, a cell’s pathway may change depending on
the cellular environment in which it is placed, as well as its internal mechanism
system. (Marieb,E,Hoehn,K.2007)
Spermatogenesis is the maturation of male gametes (sperm cells) in the testes
which takes places within the seminiferous tubules, where primary spermatocytes
mature to become mature sperm cells. Developing gametes mature and are atored
until ejaculation. Mature sperm cells are then able to fertilize the counterpart female
gamete, the oocyte, during conception to produce a single-celled individual known as
a zygote. This process begins with spermatogonia; stem cells that remain in the
seminiferous tubules for sperm production. This is the cornerstone of sexual
reproduction and involves the two gametes contributing half the normal set of
chromosomes (haploid, n) to result in a chromosomally normal (diploid, 2n) zygote.
(Williams,G.2003)
SAMPLE 2 – STUDENT WORK
Factors affecting growth and reproduction
There are many factors that can affect growth and reproduction in humans such as
nutritional deficiencies and being underweight or overweight.
Nutrients are substances in food used by the body to enable normal growth,
maintenance and repair. A child who does not receive adequate nutrition will be
shorter and weaker than one who eats sufficiently. Though growth depends partially
on genetics, nutrition also plays a major role. For example, a child with parents
around five and a half feet in height is unlikely to grow over six feet. However, if this
same child is malnourished, he or she runs the risk of never growing to a full
potential height. This child might reach five foot four with proper nourishment, but
could grow to only five feet or less if lacking in proper nutrition.
Reproduction may be affected by being underweight or overweight. Excessive
weight reduces fertility in both men and women. In women, this increases the
release of oestrogen which may lead to the disruption of the menstrual cycle, thus
reducing the ability to conceive. Being underweight however, can prevent ovulation
due to insufficient oestrogen release. As oestrogen is stored and used where the
body’s fat stores are, lower body weight in effect lowers the oestrogen levels.
(Williams,G.2003)
4. Primary and secondary defence mechanisms, and autoimmune disease and
allergies
The immune system performs specific defence against disease and other potentially
damaging foreign bodies. When functioning properly, the immune system identifies a
variety of threats including viruses, bacteria and parasites, whilst distinguishing them
from the body’s own tissue. Pathogens are often in contact with the skin or entering
the airway, the digestive tube and the genital orifices and mucosae. They can also
penetrate the circulation directly through wounds. The human body however is
equipped with an internal defence mechanism to defend against these pathogens by
a primary and secondary immune response. (Marieb, E, Hoehn, K.2007)
At the heart of the immune response is the ability to distinguish between ‘self’ and
‘non-self’. Every cell in the body carries the same set of distinctive surface proteins
that distinguish them as ‘self’ as seen in the diagram below. Usually, the immune
cells do not attack the body’s own tissues, which all carry the same pattern of selfmarkers; rather, the immune system coexists peaceable with the other body cells in
a state know as self-tolerance. This set of unique markers on human cells is called
the major histocompatibility complex (MHC). There are two classes: MHC Class I
proteins, which are on all cells, and MHC Class II proteins, which are only on certain
specialized cells. (Marieb,E,Hoehn,K.2007)
SAMPLE 2 – STUDENT WORK
(Guillainbarre.wikispaces.com
2014)
Any non-self substance capable of triggering an immune response is known as an
antigen. An antigen can be a whole non-self cell, a bacterium, a virus, an MHC
marker protein or even a portion of a protein from a foreign organism. The distinctive
markers on antigens that trigger an immune response are called epitopes. When
tissues or cells from another individual enter the body carrying such antigenic nonself epitopes, the immune cells react. For example, transplanted tissue may be
rejected as foreign and why antibodies will bind to them.
(Tortora,G.J,Grabowski,S.R.1999)
The primary immune response is the first encounter with a pathogen and the
subsequent reaction to it, involving white blood cells called lymphocytes.
Lymphocytes are small white blood cells which play a major role in defending the
body against disease. There are two types of lymphocytes; B-lymphocytes which
make antibodies to attack bacteria and toxins, and T-lymphocytes to help destroy
infected or cancerous cells. (Tortora,G.J,Garabowski,S.R.1999)
As lymphocytes develop, they normally learn to tell the difference between the
body’s own tissues and foreign bodies. Once B-cells and T-cells are formed, a few of
those cells will multiply and provide memory for the immune system. This allows the
immune system to respond faster and more efficiently the next time the body is
exposed to the same antigen. In many cases it will prevent sickness. For example, a
person who has had chickenpox or has been immunized against chickenpox is
immune from getting chickenpox again. (biologyguide.net 2014)
SAMPLE 2 – STUDENT WORK
Antigens trigger the production of antibodies by the immune system by Blymphocytes. When B-cells become activated due to the presence of a particular
antigen, they create antibodies that are specific to that specific antigen. Killer T-cells
and antibodies are a sub-group of T-lymphocytes that kill cells that are infected with
viruses and other pathogens. Helper T-cells help determine which immune
responses the body makes to a particular pathogen.
(Tortora,G.J,Grabowski,S.R.1999)
During the initial course of responding to antigens such as bacteria and viruses,
some T and B-lymphocytes become cells known as memory cells. These cells
enable the immune system to recognize antigens that the body has previously
encountered. Memory cells direct a secondary immune response in which immune
cells such as cytotoxic T-cells and antibodies are produced more quickly and for a
longer period of time than during the primary response. Memory cells are stored in
the lymph nodes and spleen and can remain for the life of an individual. If enough
memory cells are produced while encountering an infection, these cells can provide
life-long immunity against certain diseases such as mumps and measles.
(biologyguide.net 2014)
In abnormal situations, the immune system can wrongly identify ‘self’ as ‘non-self’
and initiate a misdirected immune attack. The result can be an autoimmune disease
such as rheumatoid arthritis, resulting in painful inflammation and deformities in
some areas. In some people, an apparently harmless substance such as ragweed
pollen or cat hair can provoke the immune system to set off the inappropriate and
harmful response known as allergies. Allergies, whether seasonal, perennial or
specific, are a response to external antigens; substances that antibodies recognize
as foreign and attack, such pollen, dust, peanuts or shellfish, among others.
(Sciencemusuem.org 2014)
Both allergies and autoimmune disease can be considered hyper-immune
responses, whereby the body’s immune system becomes supercharged, attacking or
responding to substances that should not normally draw such attention. Because
these two classes of disorders involve a misplaced inflammatory response, they also
tend to overlap somewhat with regard to symptoms. During flares of each type, one
may experience common symptoms such as redness, swelling, rash and itchiness.
This is a result of the inflammatory process occurring during each acute episode,
which are similar in some respects, but quite different in others.
(Sciencemuseum.org 2014)
SAMPLE 2 – STUDENT WORK
Reference list
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(accessed 20/04/14)
http://jeejeebhoy.ca/2010/10/12/the-hypothalamus-and-brain-injury/ (accessed
20/04/14
http://www.unckidneycenter.org/kidneyhealthlibrary/glomerulardisease.html
(accessed 20/04/14)
http://davidsblogiisb.blogspot.co.uk/2011/02/mitosis-vs-meiosis.html (accessed
20/04/14)
http://www.biology-online.org/dictionary/homeostasis (accessed 25/04/14)
http://www.bbc.co.uk/learningzone/clips/cell-division-by-mitosis-andmeiosis/6002.html (accessed 25/04/14)
http://www.biologyguide.net/unit2/2a_cell_division.htm (accessed 25/04/14)
http://www.sciencemuseum.org.uk/whoami/findoutmore/yourbody/whatdoesyourimm
unesystemdo.aspx (accessed 25/04/14)
http://guillainbarre.wikispaces.com/self+and+non-self+recognition (accessed
25/04/14)
Tortora G.J. and Grabowski S.R. (1999) Principles of Anatomy and Physiology. 9th
edition. John Wiley & Sons:New York
Fullick,A. at al (2011) AQA Science Biology. Nelson Thornes Ltd:Cheltenham
Williams,G. (2003) Advanced Biology For You. Nelson Thornes Ltd:Cheltenham
Marieb,E,Hoehn,K. (2007) Human Anatomy & Physiology. 7th edition. Pearson
Education, Inc:San Francisco