Life sciences

• The erectile tissue in the penis fills with blood during sexual arousal, causing an erection.
• DNA stands for deoxyribonucleic acid.
• The function of DNA is to control the synthesis of proteins, carry hereditary characteristics from parents to offspring, and control the structure and functioning of the cell.
• DNA mainly occurs in the nucleus where it forms part of the chromatin network/chromosomes, but it can also be found outside the nucleus.
• DNA found inside the nucleus is referred to as nuclear DNA and DNA found outside the nucleus is referred to as extranuclear DNA.
• Extranuclear DNA occurs in the mitochondria and in the chloroplast.
• Extranuclear DNA found in the mitochondria is called mitochondrial DNA and extranuclear DNA found in the chloroplast is referred to as chloroplastic DNA.
• Chloroplastic DNA and Mitochondrial DNA control the synthesis of proteins within these organelles themselves.
• Mitochondrial DNA is also helping us trace our ancestors.
• Deoxyribonucleic acid (DNA) is made up of smaller units called nucleotides.
• Nucleotides are the building blocks of nucleic acids (DNA and RNA).
• The natural shape of the DNA molecule is double helix.
• A nucleotide is made up of three parts: a sugar molecule (S), a phosphate portion (P), and a nitrogenous base (NB).
• The sugar molecule in DNA is deoxyribose sugar.
• There are four types of nitrogenous bases found in DNA: Adenine, Thymine, Cytosine, and Guanine.
• The amnion is on the inside with its amniotic cavity filled with amniotic fluid.
• The period during which the embryo develops within the uterus of the mother up to the time when the baby is born is referred to as pregnancy, also known as gestation.
• The umbilical artery carries deoxygenated blood with nitrogenous wastes from the embryo to the placenta.
• The amniotic fluid prevents drying of the embryo, keeps the foetus within a small temperature range, and allows relatively free foetal movement for growth and development.
• The umbilical cord contains the umbilical artery and umbilical vein.
• The placenta serves for attachment of the embryo to the mother, allows for diffusion of dissolved food from the mother to the foetus, allows for diffusion of oxygen from the mother to the foetus, and for the diffusion of carbon dioxide from the foetus to the mother.
• The umbilical vein carries oxygenated blood with dissolved food from the placenta to the foetus.
• Soon after attachment to the endometrium, extraembryonic membranes develop, including the chorion and the amnion.
• The chorion is on the outside and forms the chorionic villi.
• A hollow, rope-like tube called the umbilical cord attaches the embryo to the placenta.
• In humans, pregnancy lasts for about 280 days.
• The placenta also allows for the diffusion of nitrogenous excretory wastes from the foetus to the mother and secretes its own progesterone which functions to maintain pregnancy after about week 12.
• Adenine pairs with Thymine and Cytosine pairs with Guanine, hence they are said to be complementary base pairs.
• Adenine and guanine are called purines, whilst cytosine and thymine are called pyrimidines.
• The scrotum is located outside the body because it allows for temperature regulation to occur.
• Testosterone encourages sperm maturation.
• The penis is the external reproductive organ of the male.
• The optimum temperature for the production of sperms is 2 - 3 ° c lower than normal body temperature.
• At puberty, meiosis takes place in the sex organs (testes and ovaries) to produce haploid gametes.
• By making the sex cells different from each other, meiosis ensures that the offspring produced are different from each other and their parents.
• The seminal vesicles, prostate gland, and cowpers gland are the accessory glands of the male reproductive system.
• The zygote undergoes mitosis to produce millions of cells that are genetically identical.
• Since the gametes have been formed by meiosis, they are genetically different from each other and half the number of chromosomes as the original cell.
• These cells have differentiated and have become adapted to their functions.
• A lower temperature is necessary for the production of healthy sperm so that healthy sperm can survive.