Topic 2 - Cells, Viruses and Reproduction Flashcards
What is double fertilisation?
- One male gamete fuses with two polar nuclei to form triploid endosperm nucleus
- One male gamete fuses with female gamete to form diploid zygote
2 types of gametogenesis?
Spermatogenesis
Oogenesis
Stages of spermatogenesis?
1) Primodial germ cell > Spermatogonia
2) Spermatogonia > Primary spermatocyte
3) Primary spermatocyte > Secondary spermatocyte
4) Secondary spermatocyte > Spermatids
5) Spermatids > 4 Spermatozoa
Stages of Oogenesis?
1) PGC > Oogonia
2) Oogonia > Primary oocyte
3) Primary oocyte > Secondary oocyte & 1 polar body
4) Secondary oocyte & 1 polar body> 1 ovum & 3 polar bodies
How do primary spermatocytes form ?
PGC divides by mitosis - forms spermatogonia
Then continues to grow without further division - forms primary spermatocyte
What are the male sex organs in plants and where are they found?
- Pollen
- Anthers
What and where are female sex organs in plants?
- Ovules
- Ovaries
What are the names of male and female gametes?
M - Spermatozoa
F - Ova
Define meiosis
Sexual reproduction that reproduces 4 genetically different haploid cells
How are gamete’s produced in plants?
Meiosis forms male microspores and female megaspores which then produce gamete’s
What is crossing over (recombination)
Large multi-enzyme complexes cut and rejoin parts of the maternal and paternal chromatids at the end of prophase 1
How does a pollen grain form in the anther ?
1) Meiosis of diploid microspore cells in the anther forms 4 haploid microspores
2) Haploid microspores mature into pollen grains via mitosis
Describe structure of pollen grain
- Outer protective coating
- Pollen tube cell (which has its own nucleus) elongates to penetrate ovule
Rough endoplasmic reticulum
- A series of flattened sacs enclosed by a membrane with ribosomes on the surface
- Folds and processes proteins made on the ribosomes
Smooth endoplasmic reticulum
- A series of membrane bound sacs
- Synthesises and processes lipids and steroids
Golgi apparatus
- A series of fluid-filled, flattened and curved sacs called cisternae, with vesicles surrounding the edges
- Sorts, processes and packages proteins and lipids
- Also produces lysosomes
Mitochondria
- Oval-shaped and bound by a double membrane called the envelope
- Inner membrane folded to form projections called cristae, with matrix on the inside containing the enzymes needed for cellular respiration
Centrioles
- Hollow cylinders containing a ring of microtubules arranged at right angles to each other
- Involved in cell division
80S ribosomes
- Large subunit (60S) and small subunit (40S)
- Site of protein synthesis
Lysosomes
- Vesicles containing digestive enzymes bound by a single membrane
Features of eukaryotic cells
- Nucleus
- RER
-SER - Golgi apparatus
- Mitochondria
- Centrioles
- 80S ribosomes
- Lysosomes
Features of prokaryotic cells
- Cell wall
- Slime capsule
- Plasmid
- Flagellum
- Pili
- 70S ribosomes
- Mesosomes
Cell wall
Rigid outer covering made of peptidoglycan
Provides the cell with strength and support
Slime capsule
Protective slimy layer which helps the cell to retain moisture and adhere to surfaces
Plasmid
Circular piece of DNA
Flagellum
A tail-like structure which rotates to move the cell
Pili
Hair-like structures which attach to other bacterial cells and allow plasmids to move from cell to cell
70S ribosomes
- Large subunit (50S) and small subunit (30S)
- Site of protein synthesis
Mesosomes
Infoldings of the inner membrane which contain enzymes required for respiration
Gram positive bacteria cell wall
- Thick layer of peptidoglycan
- Inner plasma membrane
Gram negative bacteria cell wall
- Thin layer of peptidoglycan layer
- Outer lipopolysaccharide membrane
Magnification
How much bigger the image is comapred to the original object
Resolution
How far apart two points can be before they are seen as one
Types of microscopes
- Optical (light, objective lens and eyepiece lens magnify)
- Scanning electron (3D image, beam of electrons scan back and forth over surface of sample/dead specimen)
- Transmission electron (Beam of electrons transmitted through object, 2D image, very thin sample)
Describe virus and its structure
- Non-living structures
- Consist of a nucleic acid (DNA or RNA)
- Enclosed in protective coat (capsid)
- Sometimes covered with lipid layer (envelope)
Ethical implications to using/not using untested drugs
- Difficult to obtain informed consent
- Unknown side effects
- May not be as effective as the currently accepted treatment
Lysogenic cycle
- Virus inserts DNA into DNA of the host cell
- DNA replicated via cell division of host cell
- Can stay dormant
- Can lyse
Lytic cycle
- Insert DNA/RNA into cytoplasm of host cell
- Viral genome is replicated independently of the host cell genome
- Leads to lysis of the host cell when a large number of viruses are assembled and ready to infect more cells
Why would dormant viruses enter the lytic pathway
If the lysogenic host cell becomes damaged or the immune system becomes weak
Mitosis
Produces 2 genetically identical daughter cells for growth, repair and asexual reproduction
Stages; Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis
Prophase
- Breakdown of nuclear membrane
- Spindle fibres appear
- Chromosomes condense
Metaphase
- Spindle fibres attach to chromosomes
- Chromosomes condense
- Chromosomes align
Anaphase
- Centromeres divide
- Sister chromatids move to opposite poles
Telophase
- Nuclear membrane reforms
- Chromosomes decondense
- Spindle fibres disappear
Cytokinesis
- Cytoplasm divides
- Parent cell becomes 2 daughter cells with identical genetic information
Interphase
- Growth
- DNA replication
- Preparation for division
Meiosis
Produces 4 genetically different daughter cells
2 ways genetic variation is achieved
1) Crossing over - the exchange of sections of DNA between homologous chromosomes
2) Independent assortment - there are various combinations of maternal and paternal chromosome arrangement
Chromosome mutations
1) Translocations - where a part of 1 chromosome breaks off and reattaches to another completely different chromosome. Balanced or unbalanced
2) Deletion
3) Inversion
4) Substitution (frame shift)
5) Non-disjunction - homologous chromosomes or sister chromosomes fail to separate, resulting in either polysomy (more than 2 chromosomes in a cell e.g. down syndrome) or monosomy (less than 2 chromosomes in a cell e.g. turner syndrome)
How is the ovum specialised
- Zona pellucida - protective coating that sperm has to penetrate for fertilisation (prevents polyspermy)
- Contains haploid nucleus
- Cortical granules - release substances which cause zona pellucida to harden forming a tough fertilisation membrane
- Follicle cells form a protective coating around the egg
Spermatozoa adaptations
- Contain mitochondria to provide energy for movement
- Acrosomes contain digestive enzymes which break down the zona pellucida
- Haploid nucleus
Fertilisation in animals
1) Sperm head contacts zona pellucida and acrosome reaction occurs (digests zona pellucida)
2) Sperm head fuses with cell membrane of the egg cell, allowing the sperm nucleus to enter egg cell
3) Cortical reaction occurs causing zona pellucida to harden and prevent polysomy
4) Nuclei fuse and a full set of chromosomes restores, forming diploid zygote
Pollen formation
1) Diploid microspore mother cells in the anther undergo meiosis. They form 4 haploid microspores
2) Haploid microspores undergo mitosis to mature to pollen grains
(pollen grains have 2 nuceli, generative nucleus and pollen tube nucleus and protective coating)
Ovum formation in plants
1) Diploid megaspore mother cells in ovule undergo mitosis forming ootid and 3 polar bodies which degenerate and are reabsorbed
2) Ootid undergoes 3 mitotic divisions to form embryo sac
(embryo sac has 2 polar nuclei from endosperm, an egg cell which forms zygote, 2 synergids (help generative nucleus reach egg cell) and 3 antipodal cells (no established function) with protective covering)
Fertilisation in plants
1) Pollen grain composed of the pollen tube nucleus and the generative nucleus adheres to the stigma, where it germinates
2) Pollen tube grows down the style via the secretion of digestive enzymes which digest surrounding tissue and use it as a source of nutrients
3) Pollen tube grows through micropyle into embryo sac
4) Generative nucleus of pollen divides by mitosis to produce 2 sperm cells which enter embryo sac
5) Double fertilisation occurs
