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Flashcards in SNS Biology - Embryology Deck (30):
1

Development in Vertebrates
Fertilisation
 

•    Can occur 12-24 hrs after ovulation
•    Happens in lateral, widest portion of oviduct
 

2

Cleavage

•    Rapid mitotic divisions that occur shortly after fertilisation
•    Leads to an increase in cell number without corresponding growth in protoplasm (cell volume)
•    Also increases surface-to-volume ratio for each cell, improving gas and nutrient exchange
 

3

Cleavage
Indeterminate Cleavage
 

•    Cleavage that results in cells that maintain ability to develop into a complete organism
•    Identical twins are the result of determinate cleavage
 

4

Cleavage
Determinate Cleavage
 

•    Cleavage resulting in cells whose future differentiation pathways are determined

5

Development in Vertebrates

1.    Fertilisation
2.    Cleavage
3.    Morula Formation
4.    Blastulation
5.    Gastrulation
 

6

Development in Vertebrates
Cleavage
 

1.    First complete cleavage of the zygote occurs ~32 hrs after fertilisation
2.    Second cleavage after 60 hrs
3.    Third cleavage after 72 hrs at which point the at which point the eigth celled embryo reaches the uterus
 

7

Development in Vertebrates
Morula Formation
 

As cell division continues, a solid ball of embryonic cells, the morula, is formed

8

Development in Vertebrates
Blastulation
 

•    Begins when the morula develops a fluid filled cavity called the blastocyst
•    By the fourth day, becomes a hollow sphere of cells called the blastula
•    At this stage the embryo adheres to the uterine wall
 

9

Development in Vertebrates
Gastrulation
 

•    Once implanted in the uterus, cell migrations transform the single-cell layer of the blastocyst into a three layered structure called the gastrula

10

Development in Vertebrates
Types of Development
 

1.    External
2.    Internal non-placental
3.    Internal placental
 

11

Development in Vertebrates
Types of Development
External
 

•    Early development of many animals occurs outside of the mother’s body
•    For example fish and amphibians lay eggs that are fertilised externally. Reptiles and some mammals (duck billed platypus) develop externally on land
 

12

Development in Vertebrates
Types of Development
External
Embryonic Membranes
 

1.    Allantois
2.    Amnion
3.    Chorion
4.    Yolk Sac
 

13

Development in Vertebrates
Types of Development
External
Embryonic Membranes
Allantois
 

Sac-like structure involved in respiration and excretion. Contains blood vessels to transport O2, CO2, water, salt and nitrogenous waste

14

Development in Vertebrates
Types of Development
External
Embryonic Membranes
Amnion
 

Membrane enclosing amniotic fluid. Latter provides an aqueous environment that protects the developing embryo from shock

15

Development in Vertebrates
Types of Development
External
Embryonic Membranes
Chorion
 

Lines the inside of the shell. Moist membrane permitting gas exchange

16

Development in Vertebrates
Types of Development
External
Embryonic Membranes
Yolk Sac
 

Encloses the yolk. Blood vessels in the yolk sac transfer food to the developing embryo

17

Development in Vertebrates
Types of Development
Internal Non-placental
 

•    Certain animals develop in the mother without a placenta
•    For example, marsupials, some tropical fish
•    Without a placenta, exchange of food and oxygen is limited
•    Offspring may be born very young
 

18

Development in Vertebrates
Types of Development
Internal Placental
 

•    Growing foetus receives O2 directly from its mother via specialised circulatory system
•    Not only supplies O2 and nutrients, but removes CO2 and metabolic waste
•    Two key components are umbilical chord and placenta which both develop in the first few weeks after fertilisation
 

19

Development in Vertebrates
Types of Development
Internal Placental
Development
 

•    Umbilical chord and placenta  develop in the first few weeks after fertilisation
•    Outgrowths of the four extra-embryonic membranes formed during development – amnion, chorion, allantois and yolk sac
 

20

Development in Vertebrates
Types of Development
Internal Placental
Development
Amnion
 

Thin, tough membrane containing amniotic fluid – shock absorber for external pressure and localised pressure during labour and childbirth

21

Development in Vertebrates
Types of Development
Internal Placental
Development
Chorion
 

Membrane which completely surrounds the amnion

22

Development in Vertebrates
Types of Development
Internal Placental
Development
Allantois
 

Membrane which develops as an outpocketing of the gut. Blood vessels of the allantoic wall enlarge and become the umbilical vessels which connect the foetus to the placenta

23

Development in Vertebrates
Types of Development
Internal Placental
Development
Yolk Sac
 

Site of early development of blood vessels. Becomes associated with the umbilical vessels

24

Development in Vertebrates
Birth
Labour
 

•    Series of strong uterine contractions
1.    Three stages:
1.    Cervix thins and dilates, amniotic sac ruptures. Contractions mild
2.    Rapid contractions, birth of baby
3.    Uterus contracts, expelling the placenta and umbilical cord
 

25

Plant Embryology
Seed Formation
 

Zygote divides mitotically to form the mass of cells called the embryo

26

Plant Embryology
Seed Formation
Embryo Components
 

1.    Cotyledons – seed leaves. Dicots have two, monocots (grasses) have one
2.    Epicotyl – precursor of the upper stem and leaves
3.    Endosperm – grows and feeds the embryo. In dicots, the cotyledon absords the endosperm
4.    Hypocotyl – develops into the lower stem and root
5.    Seed coat – outer coating of the ovule. Embryo and seed coat together comprise the seed
 

27

Plant Embryology
Seed Dispersal
 

•    Fruit in which most seeds develop is formed from the ovary walls, base of flower and other consolidated pistil components
•    Serves as means of dispersal, allowing to be carried by air, water or animals
 

28

Plant Embryology
Plant Development
 

•    Growth in higher plants is restricted to the meristem (embryonic, undifferentiated) cells
•    Gradually, these elongate and differentiate into cells types characteristic of the species
 

29

Plant Embryology
Plant Development
Apical Meristem
 

Found in the tips of roots and stems. Growth in length occurs only at these points

30


Plant Embryology

Plant Development

Latersl Meristem

•    Or cambium
•    Located between the xylem and phloem.
•    Permits growth in diameter and can differentiate into new xylem and phloem cells
•    Not an active tissue in monocots (grasses) or herbaceous dicots (alfalfa) but is predominant in woody dicots (eg oaks)
 

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