Male Reproductive System

• The reproductive system is responsible for reproduction and differs greatly between males and females despite being formed from the same embryological structures and sharing the same hormones.
• These hormones are testosterone, estrogen, and progesterone, with varying quantities producing different responses in males and females.
• The system is not fully formed until puberty.

Male Reproductive System

• Responsible for secretion of male sex hormones and sperm and for the transfer of sperm cells.
• Secondary male characteristics develop between the ages of 10-14 years old.
• Testes produce sperm and testosterone.
• The epididymis matures and stores sperm.
• Sperm or ejaculatory duct transports sperm from the epididymis to the urethra.
• Seminal vesicles, Cowper’s gland, and the prostate gland produce seminal fluid to feed sperm and allow them to swim, collectively called semen.
• The urethra allows passage of either urine or sperm.
• The penis places sperm inside the female's body and is responsible for urination and ejaculation.
• The scrotum maintains the testes at the optimal temperature 35° for meiosis, which produces sperm cells.

Female Reproductive System

• Responsible for producing female sex cells and hormones, receiving sperm and for the development and nourishment of the fetus.
• Secondary female characteristics develop during the ages of 10-14 years old.
• The ovaries produce eggs (ova), estrogen, and progesterone.
• The fallopian tube (oviduct) catches eggs from the ovary and transports them to the uterus where fertilization occurs.
• The uterus is the site of implantation and holds the developing embryo, with a lining (endometrium) enriched with blood vessels to nourish the embryo and form the placenta.
• Implantation is where the egg attaches to the uterus itself.
• The vagina allows entry of sperm and exit of the baby at birth and is covered by a layer of hymen.

Role of Hormones

• Hormones regulate reproduction and react and adjust due to environmental changes.
• In the male reproductive system, the prostate glands produce hormones that nourish sperm cells and help them mature.
• The testes produce hormones that regulate the production and release of sperm cells.
• In the female reproductive system, follicles produce hormones that control the growth and release of eggs from the ovaries.
• The ovaries produce progesterone, which prepares the uterus for pregnancy.
• The hypothalamus produces oxytocin, which controls vaginal dilation during childbirth.

Endocrine System

• Responsible for hormone production and secretion.
• Hormones are special chemicals that regulate growth, development, metabolism, reproductive processes, and mood, affecting almost every aspect of the human body.
• It secretes hormones into the bloodstream, where they are carried throughout the body.
• When hormones reach their target organ, that organ responds and functions according to that response.
• It sends signals throughout the body through hormones, but takes a long time (hours to weeks) to occur.
• Hormonal imbalances may cause irregularities.
• The adrenal glands secrete aldosterone, which regulates salt and water balance and blood pressure.
• Corticosteroid controls key functions in the body, has anti-inflammatory properties, maintains blood sugar levels, blood pressure, and muscle strength and regulates salt and water balance.
• Epinephrine increases heart rate, oxygen intake, and blood flow.
• Norepinephrine maintains blood pressure.
• The pituitary gland secretes antidiuretic hormone, which affects water retention in kidneys and controls blood pressure.
• ACTH controls production of sex hormones and eggs in women and sperm in men.
• GH affects growth and development, stimulates protein production, and affects fat distribution.
• LH and FSH controls production of sex hormones and eggs in women and sperm in men.
• Oxytocin stimulates the contraction of the uterus and milk ducts in the breast.
• Prolactin initiates and maintains milk production and impacts sex hormone levels.
• TSH stimulates the production and secretion of thyroid hormones.
• The kidneys secrete renin and angiotensin which controls blood pressure, both directly and by regulating aldosterone production.
• The pancreas secretes glucagon, which increases blood sugar levels.
• Insulin lowers blood sugar levels and stimulates the metabolism of glucose, protein, and fat.
• The ovaries secrete estrogen, which affects female sexual characteristics and reproductive development, is important for functioning of the uterus and breasts, and protects bone health.
• Progesterone stimulates the lining of the uterus for fertilization and prepares the breast for milk production.
• The testes secrete testosterone, which develops and maintains male sexual characteristics and maturation.
• The parathyroid glands secrete parathyroid hormones which regulate blood calcium levels.
• The thyroid secretes thyroid hormone, which controls metabolism and also affects growth, maturation, and nervous system activity.
• The pineal gland secretes melatonin at night to control and regulate sleep.
• The hypothalamus secretes growth hormone releasing hormone which regulates growth hormone release.
• Thyrotropin releasing hormone regulates thyroid-stimulating hormone release.
• Gonadotropin releasing hormone regulates LH/FRH production.
• Corticotropin releasing hormone regulates adrenocorticotropin release.
• The thymus contains humoral factors and helps develop the lymphatic system.

Homeostasis

• Homeostasis is the state of steady internal physical and chemical conditions maintained by hormones.
• A stable range that bodily systems follow to ensure proper functioning.
• It is a biological equilibrium.
• It occurs with the help of the hypothalamus, as it regulates bodily processes (i.e., body temperature, thirst, and heart rate) to maintain homeostasis.
• Homeostasis functions through feedback mechanisms, namely, negative feedback and positive feedback.
• Negative feedback occurs when the product of a reaction leads to a decrease in that reaction and is a counter-response to a reaction
• When conditions go above a certain limit, negative feedback tells the body to perform a certain action to decrease that condition back to its limit.
• Positive feedback occurs when the product of a reaction leads to an increase in that reaction and amplifies the body’s response to a stimulus.

Nervous System

• Consists of the brain, nerves, and the spinal cord.
• It receives information and sends signals.
• The cells of the nervous system are the neurons.
• The nervous system is divided into the central nervous system (CNS), which encompasses the brain and spinal cord and controls bodily functions.
• Peripheral nervous system (PNS) encompasses nerves and anything else outside the brain and spinal cord, carries information from the central nervous system and delivers it to our body parts.

Neurons

• Neurons are the cells of the nervous system and consist of dendrites, which receive information and pass it to the cell body (soma).
• The cell body (soma) contains the nucleus and organelles.
• Axon takes signals away and transports them to other neurons, muscles, and tissues.
• Sensory neurons receive information consisting of mechanoreceptors (mechanical stimuli), thermoreceptors (thermal stimuli), pain receptors (harmful stimuli), chemoreceptors (chemical stimuli), and photoreceptors (light stimuli).
• Interneurons process information.
• Motor neurons cause actions in the muscles and glands or movement in general.

Nucleic Acids

• Nucleic acids are large biomolecules that carry information and make up genetic material.
• Long-chain polymeric molecules that are made up of nucleotides.
• Nucleotides are monomers/organic molecules consisting of a nitrogenous base, a pentose (5-sided) sugar, and a phosphate.
• There are two types of nucleic acids: RNA and DNA.
• Ribonucleic acid (RNA) is a single-stranded nucleic acid and is responsible for a majority of protein synthesis processes in cells, consisting of messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).
• Messenger RNA (mRNA) carries genetic code from DNA to the ribosome.
• Transfer RNA (tRNA) carries amino acids to the ribosome based on the codons of the RNA chain.
• Ribosomal RNA (rRNA) is a component in the large and small unit of the ribosome.
• Deoxyribonucleic acid (DNA) is a double-stranded nucleic acid and carries genetic information.

Central Dogma of Molecular Biology

• A theory that illustrates the process in which the information in DNA is converted into a functional product. Also known as gene expression.
• States that genetic information flows from DNA to RNA to protein.
• It involves three processes: DNA replication, translation, and transcription.

DNA Replication

• The process wherein a strand of DNA makes two copies of itself and is an enzyme-catalysed reaction.
• It begins at the replication fork, or the site of unwinding. The DNA unwinds because of the enzyme Helicase.
• The individual strands of DNA are the parent strands.
• Then, DNA Polymerase adds complementary bases to the parent strands (a.k.a. DNA synthesization)
• DNA synthesization is always unidirectional in the 3’→ 5’ direction.
• In one strand (leading strand) it is continuous replication, while in the other strand (lagging strand), it is discontinuous replication.
• The leading strand is headed in the 3’→ 5’ direction.
• The lagging strand is headed in the 5’→ 3’ direction, which causes Okazaki fragments or gaps in the complementary bases.
• Enzyme DNA Ligase’s job is to join them together.
• Coding strand of DNA: 5’ ATG TAT GCC AAT GCA 3’
• Runs in the 5’→ 3’ direction
• Template strand of DNA: 3’ TAC ATA CGG TTA CGT 5’
• Runs in the 3’→ 5’ direction.
• Opposite to coding strand.
• Thymine pairs with Adenine, and vv. (T → A, A → T)
• Guanine pairs with Cytosine, and vv. (G → C, C → G)

Transcription

• The process of making an RNA copy of a gene’s DNA sequence.
• The enzyme RNA Polymerase attaches to DNA and moves until it detects a promoter sequence, where transcription can then begin.
• The DNA then unwinds and all the bases on the DNA strand are exposed, which is the template strand for a new mRNA strand.
• Complementary ribonucleotides are then added to the bases on the DNA (template strand).
• The RNA Polymerase then detects a terminator sequence, and transcription stops. The RNA Polymerase then releases the template strand.
• The unwinding (promoter) and rewinding (terminator) moves up the DNA strand.
• The ribonucleotides then form a continuous chain—an mRNA.
• The mRNA then heads to the ribosome.
• Each sequence of three ribonucleotides is a codon.
• mRNA strand: 5’ AUG UAU GCC AAU GCA 3’
• Runs in the 5’→ 3’ direction
• Every 3 bases is a codon

Translation

• The process through which information encoded in messenger RNA (mRNA) directs the addition of amino acids during protein synthesis
• The ribosome assembles around the mRNA to be read.
• The first tRNA, which is always attached to methionine (amino acid), attaches to the mRNA’s first codon.
• tRNA has an anticodon and a protein attached to it.
• The finished amino acid chain does not always start with methionine because the enzyme methionine aminopeptidase removes methionine in a process known as post-translational modification.
• Then, the next tRNA attaches to the next codon.
• Then, the amino acid of the previous tRNA attaches to the amino acid of the current tRNA.
• The process repeats until an amino acid chain is produced, also known as a protein.
• tRNA strand: 3’ UAC AUA CGG UUA CGU 5’
• Does not determine the amino acids
• Has an anticodon, opposite to the codons on the mRNA strand
• Runs in the 3’→ 5’ direction
• Amino Acid Sequence: Tyr — Ile — Arg — Leu — Arg

Evolution

• The process of change in living organisms over a period of time.
• The reason living things both resemble and differ from each other.

Fossil Evidence for Evolution

• The remains of prehistoric organisms are preserved through fossilization.
• Fossils can most commonly be found in sedimentary rock.
• Fossils are evidence that life on Earth has changed over time.
• Impression fossils are formed when the organism's original bone or tissue is removed after burial, resulting in a cast after the mud hardens.
• Compression fossils are formed when the weight of the sediments flattens the organism’s remains with some organic material left behind, and the most common type of fossil.
• Fossils can be dated through relative dating, where the age of the fossil is determined by the age of the sediment around it.
• Older layers have older fossils, and vice versa.
• Radioactive or absolute dating measures the decay of unstable elements into stable ones over time.
• Each radioactive element has a half-life
• Scientists compare the amount of the original radioactive element to its decay product to determine the material's age.
• Carbon dating (measuring the amount of carbon-14 isotopes) can measure fossils up to 75,000 years old.
• Other isotopes (Potassium-40 or Uranium-238) are used to date fossils over 100,000 years old.

Anatomical Evidence for Evolution

• The similarities in the structures and functions of certain body parts of different organisms.
• Homologous structures are similar body parts or organs of different organisms but have different functions.
• Structures indicate divergent evolution, where different organisms that share a common ancestor gradually lose their structural similarities, creating different but similar species.
• Analogous structures are traits that are similar in function but different in structure across different species.
• This indicates convergent evolution where different organisms evolve to have similar traits with the same functions due to their shared environment.
• Analogous structures display that similar selective pressures can produce similar adaptations

Genetic Evidence for Evolution

• All living organisms passed on their traits via DNA.
• Closely related species should be more similar to their genetic makeup compared to distantly related species.
• The greater the similarity in amino acid sequence, the closer the relationship.
• Organisms which are similar in structure must also possess biochemical similarities.

Embryological Evidence for Evolution

• Features that are developed during gestation do not always appear when organisms are fully formed.
• For example, humans and fish both have gills as embryos, but are not fully manifested in humans.

Theory

• A theory is supported by findings from repeated tests and/or experiments.

Theory of Catastrophism (Georges Cuvier)

• Earth’s biological and geographical characteristics are largely formed through catastrophes, rather than a gradual change.
• The appearance and disappearance of species occur due to catastrophes.
• Dominant species are destroyed due to a large-scale catastrophic event and are replaced by new species through evolution and adaptation.

Lamarckism (Jean-Baptiste Lamarck)

• Theory of Use and Disuse: When an organ or characteristic of an organism is used frequently, it becomes stronger and more developed. When an organ or characteristic of an organism is seldom used, it becomes weaker and degenerates.
• Theory of Needs: Organisms develop new characteristics according to their needs.
• Theory of Inheritance of Acquired Characteristics: An organism’s acquired characteristics can be inherited by their offspring, creating a domino effect in the succeeding generations.
• Adaptation drives evolution
• The theory is not accepted by scientists because it doesn’t account for all observations made on life on Earth.

Darwinism (Charles Darwin)

• Organisms with characteristics and behavior better fitted to their environment are more likely to survive.
• The fittest offspring are more likely to reproduce and thrive under the conditions of their environment.
• The traits and characteristics of the succeeding generation are likely to change because an organism whose features are less fitted to their environment are less likely to reproduce nor thrive.
• Natural selection drives evolution

Lamarckism vs. Darwinism

• Lamarckism stated life originates from permanent spontaneous generation, while Darwinism states life originates from an ancestral form.
• Organisms change characteristics via environmental adaptation in Lamarckism, while organisms change via continuous genetic variations in Darwinism.
• Species do not go extinct in Lamarckism unless due to humans, while species do go extinct based on natural selection in Darwinism.

Process of Evolution

• Non-Random Mating - individuals prefer to choose their mates without regard to their genotypes.
• When two organisms with different genotypes mate, a certain trait appears which increases the chances of mating, will result in more offspring, leading to a higher frequency of the trait in the population. Can disturb the balanced distribution of genotypes in a population.
• Mutation is when an organism with a mutation survives, there is a likely chance that the resulting offspring of that organism passes on the mutation.
• This results in different traits, causing the differentiation of genus.
• Natural Selection: Organisms with favorable characteristics (according to their environment) can survive and reproduce more. Those with disadvantageous characteristics are less likely to survive.
• Gene Flow is the movement of genes out into a different population or area, which alters the genetics of a population.
• Genetic Drift is the change or fluctuation in allele frequencies in a population due to chance events. Can be both beneficial and harmful to a species.

Gene Flow vs. Genetic Drift

• Gene flow occurs through migration and larger populations, while Genetic Drift occurs through chance/random events and in smaller populations.
• Gene flow is caused by inbreeding through migration, while Genetic Drift is caused by sudden changes or sampling errors.
• Evolution is caused through migration from Gene Flow, while Evolution is caused through bottleneck effect from Genetic Drift.

Biodiversity

• Describes the variety of life in a specific area or environment.
• Organisms in biodiversity have economic and/or ecological value and their products are sources of food, medicine, clothing, shelter, and energy.
• The balance of an ecosystem is also carefully maintained fulfilling specific roles, including the maintenance of bodies of water, the prevention of soil erosion and floods, the soil cycle and composting, the absorption of pollutants.
• The food chain also helps control population density and the stability of an ecosystem.
• A species has direct economic value if their products are sources of food, medicine, clothing shelter, and energy and the organism itself has to be consumed in order to create the product.
• A species has indirect economic value if the benefits produced by these organisms can be created without consuming the organism (e.g. a beaver building dams).
• A species has aesthetic value if they contribute to the appearance and appeal of an area and promotes tourism within the country.

Stability

• Refers to the ability of an ecosystem to withstand stresses and disturbances.
• For an ecosystem to be considered stable, it needs to have mechanisms in place that help it return to its original state after a disturbance occurs.
• Population refers to all the organisms of the same group or species that live in a specific area, which breed with one another to produce offspring and ensure continuation.
• The science which focuses on the characterization and statistical analysis of the human population refers to demography.
• Population Density refers to the number of organisms per unit area.
• Population density may be either high or low.
• Population Growth is the increase in the number of individuals in a population due to an abundance in resources and is related to the biotic potential of organisms.
• Biotic potential: The capacity of an individual or population to reproduce under ideal conditions

Exponential and Logistic Growth

• Exponential growth happens when an initial population increases by the same percentage or factor over equal time increments or generations.
• Infinite growth of a population that can be displayed as a J-shaped curve.
• Exponential growth is only possible when there are infinite resources and little to no predation, disease, and competition (e.g. algal bloom).
• Logistic Growth is when a population's growth rate decreases as population size approaches a maximum imposed by the carrying capacity.
• It accounts for the different factors that can slow down population growth.
• Occurs when an environment have few individuals (and therefore competition) and plentiful resources and is plotted in an S-shaped curve due to carrying capacity (e.g. microorganisms on a culture plate).
• Carrying Capacity determines the maximum population size of a species based on the amount of resources in its ecosystem.

Three Aspects of Biodiversity Measurement

• Ecosystem Diversity: The variations in ecosystems within an area, as well as its impact on humans and the environment.
• Species Diversity: The number of different species present in an ecosystem and relative abundance of each of those species.
• Genetic Diversity: Refers to the variations in genes between individuals of a species (differences in alleles between individuals of a species). It is caused by mutations.

Density-Dependent and -Independent Limiting Factors

• Density-Dependent Limiting Factors a factor that regulates a population's growth and is influenced by population density: diseases and parasites, competition for resources, predation, and emigration.
• Density-Independent Limiting Factors a factor that regulates a population's growth and is not influenced by population density (e.g. calamities and pollution).