2.6-cell division,diversity, organisation Flashcards
State what the cell cycle is and outline its stages
Regulates cycle of division with intermediate growth periods
Interphase
Mitosis or meiosis -nucleus dividing
Cytokinesis -cytoplasm dividing
What happens during interphase
G1- cell synthesis’s proteins for replication
S- DNA synthesises
G2-organelles divide
What is the purpose of mitosis
2 genetically identical daughter cells
Growth
Cell repair,replace for tissues in multicellular organisms
Asexual reproduction
Name the stages of mitosis
Prophase
Metaphase
Anaphase
Telophase
What happens during prophase
Chromosomes condenses -visible
Centrioles move to opposite poles of cell and firm spindle fibres so they can attach to centromere
Nuclear envelope break down
What happens during metaphase
Chromosomes align to the cell equator
What happens during anaphase
Centromere divide causing sister chromatids of separate and pulled into opposite poles of cell
What happens during telophase
Chromosomes decondense -invisible
New nuclear envelope form
What happens during cytokinesis
Cell membrane cleavage furrow forms
Division of cytoplasm as cell surface membrane fuses in the middle
How is the cell cycle regulated
Check pours
What is meiosis
Cell division that produces four genetically different haploid cells known as gametes
What are homologous chromosomes
Pair of chromosomes with genes at the same locus
1 maternal and 1 paternal
What happens during meiosis I
Prophase -homologous pair to form bivalents
Crossing over -exchange of sections of generic material
Cell divides into two
What happens during meiosis II
Independent segregation of sister chromatids
Each cell divides again, producing 4 haploid cells
How does meiosis produce generic variation
Crossing over during meiosis 1
Independent assortment of homologous chromosomes and sister chromotids result in new combination of alleles
How do cells became specialised
Some genes are expressed
While others are silenced
All because of transcription
Cells produce protein that determine their structure and function
What is a transcription factor
Protein that controls transcription of genes so that only certain parts of the DNA are expressed
How do transcription factors work
Move from the cytoplasm into nucleus
Bind to promoter region upstream of target gene
Makes it easier or more difficult for RNA polymerase to bind to gene
What is a stem cell
Undifferentiated cells that can divide indefinitely and turn into other specific cell types
Name and define the 4 types of stem cell
Totipotent-develop into any cell type
Pluripotent -can develop into any cell type excluding placenta and embryo, form all tissue types
Multi potent-few different type of cells within a certain type of tissue
Unipotent -can only develop into one type of cell
Describe 2 groups of specialised cells in blood
Erythrocytes -RBC biconcave shape, lots of haemoglobin to carry o2
Leucocytes-WBC lymphocytes, eosinophils, neutrophils to engulf foreign materials
State the relationship between a system and specialised cells
Specialised tissue ->tissue that perform
Specific function ->organs made of
Several tissue types->organ system
Describe the structure of squamous and ciliated epithelia
Simple squamous epithelium -Single smooth layer of squamous cells fixed in place by basement membrane
Ciliated epithelium -made of ciliated epithelial cell
Describe the S and F of palisade cells and guard cells in plants
Palisade cells -F-absorb light energy for photosynthesis, contain many chloroplast S-pack closely together
Guard cells
F-form stomata, when turgid open when flaccid closes
S-walls thickened by spirals of cellulose
What are meristems
Totipotent undifferentiated plant cells that can develop into various types of plant cell, including xylem vessels and phloem sieve tubes
Describe the structure of phloem tissue
Sieve tube -form a tube to transport sucrose into the dissolved form of sap
Companion cells- involved in ATP production for active loading of sucrose into sieve tubes
Plasmodesmata -gaps between cell walls where cytoplasm links, allowing substances to flow
