Biology Exam Revision PDF

Biology CHECKLIST: Topic Checkbox Cells – Eukaryotic/Prokaryotic Cells – Organelles Cells – SA: V Ratio Osmosis – Process Osmosis – Solutions DNA – Structures + Function Cell Division – Mitosis Cell Division- Meiosis Inheritance – Dominant/Recessive Inheritanc...

Biology CHECKLIST: Topic Checkbox Cells – Eukaryotic/Prokaryotic Cells – Organelles Cells – SA: V Ratio Osmosis – Process Osmosis – Solutions DNA – Structures + Function Cell Division – Mitosis Cell Division- Meiosis Inheritance – Dominant/Recessive Inheritance – Punnett Squares Inheritance – Pedigree Charts Evolution – Natural Selection Evolution – Adaptations Evolution – Speciation Evolution - Fossils Cells Prokaryotes and Eukaryotes Definition ➔ Prokaryotes are unicellular organisms that lack a membrane-bound nucleus and other membrane-bound organelles. Their genetic material is not enclosed within a nucleus, and they typically have a simpler cellular structure. ➔ Eukaryotes, on the other hand, are organisms whose cells contain a true nucleus enclosed by a nuclear membrane, along with various membrane-bound organelles, making them more complex than prokaryotic cells. Structural Differences ➔ Nucleus: Prokaryotic cells do not have a nucleus; their DNA is located in a region called the nucleoid. Eukaryotic cells have a well-defined nucleus that houses their DNA. ➔ Organelles: Prokaryotes lack membrane-bound organelles, while eukaryotes possess various organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus, which perform specialised functions. ➔ DNA Structure: Prokaryotic DNA is typically circular and consists of a single chromosome, whereas eukaryotic DNA is linear and organised into multiple chromosomes. ➔ Cell Size: Prokaryotic cells are generally smaller (0.1 to 5.0 micrometres) compared to eukaryotic cells, which can range from 10 to 100 micrometres or more. Examples ➔ Prokaryotes: Examples include bacteria (e.g., Escherichia coli) and archaea (e.g., Methanogens). ➔ Eukaryotes: Examples include animals (e.g., humans), plants (e.g., oak trees), fungi (e.g., mushrooms), and protists (e.g., amoebas). Cells Cell Organelles in Plants & Animal Cells Cell organelles are specialised structures within cells that perform specific functions essential for cellular survival. In eukaryotic cells, organelles include: ➔ Mitochondria: Responsible for energy production through cellular respiration. ➔ Chloroplasts: Found only in plant cells, these organelles conduct photosynthesis. ➔ Endoplasmic Reticulum (ER): Involved in protein and lipid synthesis; can be rough (with ribosomes) or smooth (without ribosomes). ➔ Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles. ➔ Lysosomes: Contain enzymes for digestion of waste materials and cellular debris Both plant and animal cells share many organelles, but plant cells have unique structures such as cell walls and chloroplasts, which are not found in animal cells. Cell Size and Cell Theory Cell size is crucial for maintaining efficient cellular functions. As a cell grows, its volume increases faster than its surface area, which can limit the cell's ability to transport materials in and out effectively. The Cell Theory states that: 1. All living organisms are composed of one or more cells. 2. The cell is the basic unit of life. 3. All cells arise from pre-existing cells. This theory underscores the importance of cells as the fundamental building blocks of life. The Importance of the Surface Area to Volume Ratio in Cells The surface area to volume ratio is a critical factor in cell biology. As cells increase in size, their volume grows disproportionately compared to their surface area. A higher surface area relative to volume allows for more efficient exchange of materials (nutrients, waste) with the environment. When the ratio is low, cells may struggle to obtain sufficient nutrients and expel waste, which can limit growth and function. This is why many cells remain small or adopt shapes that maximise their surface area, such as elongated or flattened forms. Osmosis Process Definition (Simple) Osmosis is the movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. This process occurs until equilibrium is reached, meaning the concentrations of solute are equal on both sides of the membrane. Applicability in Cells In biological systems, osmosis is crucial for maintaining cell turgor and overall homeostasis. Cells rely on osmosis to regulate their internal environment, ensuring that they have the right balance of water and solutes. For example, plant cells use osmosis to maintain rigidity and structure, while animal cells must manage their water content to prevent swelling or shrinking. Tonicity Comparisons Hypertonic A hypertonic solution has a higher concentration of solutes compared to the inside of the cell. When a cell is placed in a hypertonic solution, water moves out of the cell to the surrounding solution, causing the cell to shrink. This can lead to cellular dysfunction if not regulated. Hypotonic A hypotonic solution has a lower concentration of solutes compared to the inside of the cell. When a cell is placed in a hypotonic solution, water moves into the cell, leading to swelling and potentially bursting (lysis) if the influx of water is excessive. This is particularly important for cells that lack a rigid cell wall, such as animal cells. Isotonic An isotonic solution has an equal concentration of solutes compared to the inside of the cell. In this scenario, there is no net movement of water across the cell membrane, allowing the cell to maintain its shape and function without gaining or losing water. This balance is essential for cells to operate effectively. DNA Structure ➔ Double Helix Formation is structured as a double-stranded helix, where two strands twist around each other, forming a right-handed spiral. ➔ Each strand is made up of nucleotides, which consist of a sugar (deoxyribose), a phosphate group, and a nitrogenous base. The strands are held together by hydrogen bonds between the bases. Base Pairing Rule ➔ The base pairing rule states that adenine pairs with thymine (A-T) and cytosine pairs with guanine (C-G). ➔ This pairing is crucial for the stability of the DNA structure and is consistent with Chargaff's rule. Functions ➔ DNA serves as the hereditary material, containing the genetic code necessary for the development and functioning of living organisms. ➔ DNA can replicate itself, allowing genetic information to be passed from one generation to the next. ➔ DNA is involved in the synthesis of proteins through the processes of transcription and translation.  Haploid and Diploid ➔ These cells contain a single set of chromosomes (n), typical of gametes (sperm and egg cells). ➔ These cells have two sets of chromosomes (2n), which is the standard state for somatic cells in most organisms, including humans. In humans, the diploid number is 46 chromosomes, organised into 23 pairs. DNA replication ➔ DNA strands are separated at the "origins of replication" creating a "replication bubble." ➔ Helicase enzymes unwind DNA, creating two single strands as templates for new DNA strands. ➔ Primase enzyme adds a primer to the template strand, providing a starting point for DNA synthesis. ➔ DNA polymerase builds new strands by matching bases on the template strand with complementary bases. ➔ DNA is synthesised continuously and in short segments. ➔ The entire DNA molecule is copied, and RNA primers are replaced with DNA. ➔ Enzymes proofread new DNA strands for accuracy. Chromosomes structure (autosomes and homologous), functions, Alleles and genes and genome, chromatid, features, Genotype and phenotype Structure (Autosomes and Homologous) ➔ Chromosome Structure: Chromosomes are thread-like structures located within the nucleus of cells, composed of DNA and proteins. ➔ They carry genetic information essential for inheritance and cellular function.  ➔ Autosomes: Humans have 46 chromosomes, of which 44 are autosomes (the numbered chromosomes) and 2 are sex chromosomes (X and Y). ➔ Autosomes do not determine sex and are involved in various traits. ➔ Homologous Chromosomes: Each pair of homologous chromosomes consists of one chromosome from each parent. ➔ They are similar in size, shape, and genetic content, carrying genes for the same traits at corresponding loci. Functions ➔ Chromosomes store and organise genetic information in the form of genes, which are segments of DNA that code for proteins. ➔ During mitosis and meiosis, chromosomes ensure the accurate distribution of genetic material to daughter cells, maintaining genetic continuity. ➔ Homologous chromosomes can undergo recombination during meiosis, leading to genetic diversity in offspring. Alleles and Genes and Genome ➔ A gene is a specific sequence of DNA that encodes a functional product, typically a protein. Genes are the basic units of heredity. ➔ Alleles: are different versions of a gene that may produce variations in a trait. For example, a gene for eye colour may have a brown allele and a blue allele ➔ The genome: is the complete set of genetic material in an organism, including all of its chromosomes and genes. It encompasses both coding and non-coding sequences. Chromatid ➔ A chromatid is one half of a duplicated chromosome. After DNA replication, each chromosome consists of two identical sister chromatids joined at a region called the centromere. ➔ During cell division, sister chromatids are separated to ensure that each daughter cell receives an identical set of chromosomes. Features ➔ Diploid vs. Haploid: Most human cells are diploid (2n), containing two sets of chromosomes (46 total), while gametes (sperm and egg) are haploid (n), containing one set (23 chromosomes).  ➔ Genetic Polymorphism: Variants at a specific locus in the genome are called alleles, and when multiple alleles exist within a population, it is referred to as genetic polymorphism. Genotype and Phenotype ➔ The genotype is the genetic makeup of an organism, representing the specific alleles present at a given locus. It determines potential traits and characteristics. ➔ The phenotype is the observable physical and physiological traits of an organism, which result from the interaction of the genotype with the environment. For example, a plant's height or flower colour is part of its phenotype. Homozygous and heterozygous ➔ In genetics, the definition of homozygous is when you inherit the same DNA sequence for a specific gene from each of your biological parents. ➔ Heterozygous refers to having different alleles for a particular trait. Cell division Mitosis stages Interphase, prophase, metaphase, anaphase, cytokinesis Interphase ➔ Preparation Phase: Interphase is the stage where the cell prepares for mitosis. It is divided into three sub-phases: G1 (cell growth), S (DNA synthesis), and G2 (preparation for mitosis). ➔ DNA Replication: During the S phase, the cell replicates its DNA, resulting in two identical sets of chromosomes, which are essential for the next stages of mitosis. ➔ Cell Growth: In G1 and G2, the cell grows and synthesises proteins necessary for cell division. Prophase ➔ Chromosome Condensation: In prophase, the chromatin (the relaxed form of DNA) condenses into visible chromosomes. Each chromosome consists of two sister chromatids joined at a region called the centromere ➔ Nuclear Envelope Breakdown: The nuclear envelope begins to break down, allowing the chromosomes to move freely within the cell. ➔ Spindle Formation: The mitotic spindle, a structure made of microtubules, begins to form from the centrosomes, which move to opposite poles of the cell. Metaphase ➔ Chromosome Alignment: During metaphase, the chromosomes line up along the metaphase plate (the cell's equatorial plane) 3. ➔ Spindle Attachment: The spindle fibres attach to the centromeres of the chromosomes, ensuring that each sister chromatid is connected to opposite poles of the spindle. Anaphase ➔ Separation of Chromatids: In anaphase, the sister chromatids are pulled apart by the spindle fibres and move toward opposite poles of the cell. ➔ Shortening of Spindle Fibres: The spindle fibres shorten, ensuring that each new daughter cell will receive an identical set of chromosomes.  Cytokinesis ➔ Division of Cytoplasm: Cytokinesis is the final stage of cell division, where the cytoplasm of the parent cell divides, resulting in two separate daughter cells ➔ Formation of Cell Membrane: In animal cells, a cleavage furrow forms, pinching the cell membrane to create two distinct cells. In plant cells, a cell plate forms to separate the two new cells. ➔ Completion: At the end of cytokinesis, two genetically identical daughter cells are produced, each with the same number of chromosomes as the original cell. Meiosis stages Definition, Meiosis I (Interphase, prophase, metaphase, anaphase, cytokinesis), Meiosis II (prophase, metaphase, anaphase, cytokinesis), Definition ➔ Meiosis is a specialised type of cell division that occurs in sexually reproducing organisms. It results in four daughter cells (gametes), each with half the number of chromosomes compared to the original diploid parent cell. This reduction is crucial for maintaining the chromosome number across generations during sexual reproduction. Meiosis I ➔ Meiosis I is the first division in meiosis, where homologous chromosomes are separated, reducing the chromosome number from diploid (2n) to haploid (n). Interphase ➔ Before meiosis begins, the cell undergoes interphase, which includes: - G1 Phase: Cell growth and preparation for DNA synthesis. - S Phase: DNA replication occurs, resulting in duplicated chromosomes (each consisting of two sister chromatids). - G2 Phase: Further growth and preparation for meiosis. Prophase I ➔ Chromosome Condensation: Chromosomes condense and become visible. ➔ Homologous Pairing: Homologous chromosomes pair up in a process called synapsis, forming tetrads (groups of four chromatids). ➔ Crossing Over: Genetic material is exchanged between homologous chromosomes, increasing genetic diversity. ➔ Nuclear Envelope Breakdown: The nuclear envelope disintegrates, allowing the spindle apparatus to form. Metaphase I ➔ Alignment at the Metaphase Plate: Tetrads line up along the metaphase plate. ➔ Spindle Fibre Attachment: Spindle fibres attach to the centromeres of each homologous chromosome.  Anaphase I ➔ Separation of Homologous Chromosomes: The spindle fibres pull the homologous chromosomes apart, moving them toward opposite poles of the cell. Unlike mitosis, sister chromatids remain attached. Cytokinesis I ➔ Division of Cytoplasm: The cell divides into two haploid daughter cells, each containing one set of chromosomes. The nuclear envelope may reform around each set of chromosomes. Meiosis II ➔ Overview: Meiosis II resembles mitosis and separates the sister chromatids of each chromosome in the two haploid cells produced in Meiosis I. Prophase II ➔ Chromosome Condensation: Chromosomes condense again if they had decondensed after Meiosis I. ➔ Spindle Formation: A new spindle apparatus forms in each haploid cell, and the nuclear envelope breaks down if it reformed. Metaphase II ➔ Alignment at the Metaphase Plate: Chromosomes line up individually along the metaphase plate. ➔ Spindle Fibre Attachment: Spindle fibres attach to the centromeres of each sister chromatid. Anaphase II ➔ Separation of Sister Chromatids: The spindle fibres pull the sister chromatids apart, moving them toward opposite poles of the cell. Cytokinesis II ➔ Final Division of Cytoplasm: The two haploid cells divide again, resulting in a total of four non-identical haploid daughter cells (gametes), each with half the original chromosome number. Inheritance: Definitions: ➔ Inheritance refers to the process by which genetic information is passed from parents to offspring. It involves the transmission of traits and characteristics through genes, which are segments of DNA. ➔ Key Concepts: - Genes: Units of heredity that determine specific traits. - Alleles: Different versions of a gene that can exist at a specific locus on a chromosome. - Genotype: The genetic makeup of an organism. - Phenotype: The observable characteristics or traits of an organism. Co-dominant and Incomplete Dominant (Definition) ➔ Co-dominance: - Definition: A form of inheritance where both alleles in a heterozygous organism contribute equally and visibly to the phenotype. - Example: In blood type, individuals with one A allele and one B allele (genotype AB) express both A and B antigens on their red blood cells. ➔ Incomplete Dominance: - Definition: A form of inheritance where the phenotype of a heterozygote is intermediate between the phenotypes of the two homozygotes. - Example: In snapdragon flowers, crossing a red flower (RR) with a white flower (WW) produces pink flowers (RW).  Dominant and Recessive Traits (Definition) ➔ Dominant Traits: - Definition: Traits that are expressed in the phenotype even when only one copy of the allele is present (heterozygous condition). - Example: In pea plants, the allele for tall stems (T) is dominant over the allele for short stems (t). Thus, both TT and Tt plants will be tall. ➔ Recessive Traits: - Definition: Traits that are expressed in the phenotype only when two copies of the recessive allele are present (homozygous condition). - Example: The short stem trait (t) in pea plants is recessive, so only tt plants will exhibit short stems. Punnett squares How to the read it, what they are used for, examples, and functions Definition: ➔ A Punnett square is a diagram used to predict the genotypes and phenotypes of offspring from a genetic cross between two organisms. How to Read: ➔ The squares are divided into four sections (for a monohybrid cross) or more (for dihybrid crosses) representing all possible combinations of parental alleles. ➔ Each axis of the square represents the alleles contributed by each parent Uses: ➔ To determine the probability of an offspring inheriting particular traits. ➔ To visualise genetic crosses and predict outcomes of breeding experiments. Example: ➔ Consider a monohybrid cross between a homozygous dominant plant (TT) and a homozygous recessive plant (tt): Result: ➔ All offspring will be heterozygous (Tt) and exhibit the dominant phenotype.  Functions: ➔ Useful in breeding programs, genetic counselling, and studying inheritance patterns. Pedigree Charts Definition: ➔ A pedigree chart is a graphical representation of family relationships and the inheritance of specific traits across generations. How to Read: ➔ Circles represent females, and squares represent males. ➔ Shaded symbols indicate individuals expressing a trait, while unshaded symbols indicate those who do not. ➔ Lines connect parents to their offspring, showing the lineage. Uses: ➔ To track the inheritance of genetic traits and disorders within a family. ➔ To identify carriers of recessive traits and assess the risk of passing on genetic conditions. Example: ➔ A simple pedigree chart showing a trait (e.g., a genetic disorder) inherited through generations: ➔ In this example, the filled circles/squares indicate individuals with the trait, and lines show familial connections. Functions: ➔ Assists in genetic counselling and understanding hereditary diseases. ➔ Useful for researchers studying population genetics and inheritance patterns. Evolution: Natural selection Definition, Selective pressures, examples in real life Definition Natural selection is a fundamental mechanism of evolution, described as the process through which organisms better adapted to their environment tend to survive and produce more offspring. This process leads to the gradual evolution of species as advantageous traits become more common in a population over generations. Selective Pressures Selective pressures are environmental factors that influence the survival and reproduction of organisms. These pressures can include predation, competition for resources, climate changes, and disease. For example, in a habitat where food is scarce, animals with traits that allow them to find food more efficiently will have a higher chance of survival and reproduction, thereby passing those advantageous traits to their offspring. Examples in Real Life Real-life examples of natural selection include: ➔ Peppered Moths: During the Industrial Revolution in England, the coloration of peppered moths shifted from light to dark due to pollution darkening tree bark, making darker moths less visible to predators. ➔ Antibiotic Resistance: Bacteria that develop resistance to antibiotics survive and reproduce, leading to populations of antibiotic-resistant bacteria, which poses significant challenges in medicine. Adaptations Convergent and divergent Convergent Adaptation Convergent adaptation occurs when unrelated species evolve similar traits or adaptations in response to similar environmental pressures, despite having different evolutionary origins. An example is the development of wings in birds and bats; both serve the purpose of flight but evolved independently. Divergent Adaptation Divergent adaptation occurs when related species evolve different traits or adaptations due to differing environments or ecological niches. This can lead to the development of new species from a common ancestor. An example is the variation in beak shapes among Darwin's finches, which adapted to exploit different food sources on the Galápagos Islands. Speciation The Process of Speciation ➔ Causes offspring of one common ancestor to diverge in traits until they each become an entirely new species ➔ Three-step process between a common ancestor and the production of a new species ➔ A new species can be identified by the inability to breed healthy offspring between two unique organisms Step 1: Variation ➔ Variation is necessary for the process of natural selection, as the presence of mutations are required for a species to eventually adapt to their environment over time ➔ For variations and mutations to be passed down, they must first already be present within the population Step 2: Geographical Isolation ➔ There are many natural circumstances which can result in the separation of a population into two or more groups (changes in river, migration, continental drift) ➔ Due to natural selection, the two populations will develop different adaptations over time, due to the different selective pressures present in their environment.  Step 3: Isolation ➔ Gene flow from one population is no longer able to be spread to other populations. ➔ Interbreeding becomes unachievable for various reasons (sterility, incompatibility, sexual selection, different behaviours) ➔ Therefore, the two populations are now two completely different species, evolving differently from one common ancestor Theories of evolution Definition The theories of evolution explain the processes that lead to the diversity of life on Earth. They describe how species change over time through mechanisms such as natural selection, genetic drift, and mutations, resulting in new species and adaptations to their environments. Purpose The purpose of evolutionary theories is to provide a scientific framework for understanding the development of life forms, their relationships, and how they adapt to changing environments over time. These theories help explain the similarities and differences among organisms and guide research in fields like genetics, ecology, and palaeontology. Lamar’s Theory (1809) Jean-Baptiste Lamarck proposed his theory of evolution in 1809, which emphasised the idea of inheritance of acquired characteristics. He suggested that organisms could pass on traits acquired during their lifetime to their offspring. For example, he hypothesised that giraffes developed long necks because their ancestors stretched to reach higher leaves, and this acquired trait was inherited by future generations. Although Lamarck's ideas were later challenged, they contributed to early discussions about evolution. Darwin’s Theory (1859) Charles Darwin published his theory of evolution in 1859, known as natural selection. He proposed that individuals with favourable traits are more likely to survive and reproduce, leading to the gradual evolution of species over time. Key concepts of Darwin's theory include: ➔ Variation: Individuals within a species exhibit variations in traits. ➔ Survival of the Fittest: Those with advantageous traits survive and reproduce more successfully. ➔ Descent with Modification: Over generations, favourable traits become more common in the population. Fossology What is that, how its applied in real life, fossils, similar structures, homologous structures What is that? Fossology is the study of fossils, remnants or traces of ancient organisms preserved in geological formations. It provides insights into the history of life on Earth, including the evolution of species and changes in ecosystems over time. How It's Applied in Real Life Fossology is applied in various fields, such as palaeontology, archaeology, and geology. It helps scientists understand evolutionary processes, historical biodiversity, and environmental changes. Fossils are used to date geological layers and reconstruct past climates, aiding in resource exploration (e.g., oil and minerals) and conservation efforts. Fossils Fossils can include bones, teeth, shells, imprints, and even traces like footprints. They provide direct evidence of past life forms and their characteristics, allowing scientists to study the morphology, behaviour, and environment of extinct species. Similar Structures Fossils often reveal similar structures among different species, indicating common ancestry. These similarities can be observed in bone structures, dental patterns, and other physical traits, helping to trace evolutionary relationships. Homologous Structures Homologous structures are anatomical features in different species that share a common evolutionary origin, despite differing functions. For example, the forelimbs of mammals, birds, and reptiles exhibit similar bone structures, indicating they evolved from a common ancestor. This concept supports the theory of evolution by demonstrating how species adapt their structures for different environments and purposes.